Summary

Article 1. General Provisions and Definition of Terms
Article 2. Service Agreement
Article 3. Fees, Costs and Charges
Article 4. Conditions of Carriage
Article 5. Administrative Formalities/Governing Laws/Amendments/Fraud
Article 6. Discharge/Extinguishment of Obligations
Article 7. Liability for Damage
Article 8. Dispute Resolution

Article 1. General Provisions and Definition of Terms

Parties and description of cooperation. These Terms & Conditions regulate the legally binding relationship between us, the private limited company __legalName__ s.r.o., company ID No.: 29352886, with registered office at Palachovo namesti 797/4, Post Code 625 00 Brno, the Czech Republic, registered in the Commercial Register maintained by the Regional Court in Brno, file no. C 74565, Tax ID No. CZ29352886 (“__legalName__”,“We”, “Our”, “Us”), you as Our customer (“You”, “Your”, “Yourself”); (“You”, “ Your” and/or “Yourself” can also be used to refer to a passenger to be transported in a plane under the Contract of Carriage) and KAYAK Software Corporation, a Delaware corporation with offices at 7 Market Street, Stamford, CT 06902 (“ KAYAK”).

KAYAK operates the website www.kayak.com (with the respective national subdomains) where KAYAK is a travel search engine and searches other travel sites to help customers find Flights. KAYAK provides in cooperation with __legalName__ to its customers a facilitated booking path for Flight related services directly on the kayak.com website or KAYAK mobile application and sites. In the course of this cooperation, KAYAK provides search results to the prospective customers of __legalName__ and if a customer chooses to make a Booking, __legalName__ processes the Booking and provides all post Booking customer services.

In the process of the Booking, You will enter into two separate agreements; one concluded with __legalName__ for the provision of booking, payment processing, customer support and other services related with your travel; and a separate Contract of Carriage concluded with the respective Carrier(s), which you choose for Your travel. KAYAK provides the platform for searching for Flights and facilitates the Booking the Flights with Us but is not a party to the process of Booking and provision of post Booking services. In the course of Our cooperation with KAYAK we act and present Us together under KAYAK branding in order to prevent confusion or any inconvenience to You. This fact, however, does not affect the above-specified nature of Our cooperation with KAYAK.

You will not enter into any agreements or relationships with KAYAK related to the Booking of the Flight. KAYAK will not be responsible for processing the Booking or provision of post Booking services. You hereby release and discharge KAYAK from any and all liability for any claim of any kind relating to the processing of the Booking or provision of post Booking services.

Definition of Terms. The terms in BOLD listed below, and used throughout these Terms & Conditions refer to the following:

Booking: means the purchasing process of selected Flight(s), which includes the following (i) Your selection of the Flight(s) listed on the Website, (ii) completing the information required in the online form on the Website, (iii) Your acceptance of the hereunder stated Terms & Conditions and immediate performance of Services, (iv) sending Us the completed online form, (v) and making payment of the Full Price through the appropriate payment method. By making the Booking, You accept the offer of Our Services. The Booking is completed by Our acceptance of Your payment made in accordance with this Art. 1.2.1 (v) and 3.1 hereof.
Contract of Carriage: means the agreement on carriage and related services concluded between You and the Selected Carrier(s) on the basis of the provisions of Our brokerage services provided upon the Service Agreement in accordance with the provision of Art. 2.13 hereof.
Destination: means the airport You choose from the offers listed on the Website and which is, according to Your Booking (see Art. 1.2.1 hereof), the last airport on Your one-way journey. You can also order carriage back from the Destination to the original place of departure in the form of a round-trip. You can order with Us also carriage for more than one Destination in a single Booking in the form of Multi-city carriage, further defined in Art. 1.2.8 hereof. The carriage to the Destination can also be arranged for two or more Flight Connections – see Art. 1.2.5 hereof.
Flight or Flights: means an offer of carriage by air to the Destination via Selected Carrier(s). We display the offered Flight(s) on the Website. ‘Flight’ can also be used to mean two or more Flights to carry You to Your Destination.
Flight Connections : means a form of carriage wherein You will need to exit the plane at each given airport and either change planes, or re-board, in order to reach Your Destination.
Full Price: the price that We charge You for the provision of the Services and the price for the Flight ticket(s). The Full Price is further defined in Art. 3.1 hereof.
Optional Services: means the additional services related to Your Flight(s) that are offered by the Selected Carriers and/or any other third party, such as preferred meals, checked luggage, preferred seat selection, Flight/passenger’s name change, priority boarding, etc. The fee for providing Optional Services is not included in the Full Price.
Multi-city: means a form of carriage which includes a combination of Flights which pass through alternative routes on the outbound and inbound leg of a journey to Your Destination; or a form of carriage where the Destination and/or the original place of departure are different on Your return journey: e.g. JFK-LAX, SFO-JFK or JFK-LAX, LAX-SEA or JFK-LAX, SFO-SEA.
Alternatively, it can refer to a combination of Flights wherein You spend more than 24 hours in a given city, before continuing Your journey: e.g. LAX-SFO(3 day stay)-JFK & JFK-SFO(2 day stay)-LAX.
PNR: means (Eng. Passenger Name Record) is a code identifying Flight reservation(s), passenger and itinerary information. It may consist of any combination of numbers and/or letters and one PNR may include the information about the type of Flight ticket(s), date of travel, number of bags, seating information related to one or more Flights operated by one or more cooperating airlines. The PNR can always be found on the e-Ticket or boarding pass. The PNR in any circumstances does not constitute a __legalName__ and/or KAYAK order number. You should note that when travelling with multiple airlines the PNR may vary between Flights. This also applies to return Flights.
Selected Carrier: means an airline providing the services of carriage by air with which You enter into the Contract of Carriage through the use of Our brokerage services. The identity of the Selected Carrier will be made known to You before You enter into the Service Agreement with Us. Your Flight(s) may include the services of two or more Selected Carriers – where this is the case, the term Selected Carrier will be used to mean the airline carrying You across the relevant part of Your route. Please note that the actual operating carrier may differ from the Selected Carrier with which You have entered into the Contract of Carriage and as such, You must verify the identity of the operating carrier at the airport for the relevant route before departure.
Service or Services: means the brokerage services directly related to the carriage of You and Your luggage to a Destination which We provide You in accordance with these Terms & Conditions and the Service Agreement for the pre-arranged and agreed fee, included in the Full Price. Our Services, through which You will be able to conclude the Contract of Carriage with the Selected Carrier(s) are defined in Art. 2.1 hereof. Please note that Our fee, which is included in the Full Price, is related solely to the provision of brokerage Services.
Service Agreement: means the agreement on provision of the Services concluded between You and Us in accordance with Art. 1.2.1. hereof, i.e. the Service Agreement is concluded upon Your receipt of Our confirmation e-mail accepting Your payment. The purpose of the Service Agreement is to set forth the contractual relationship between You and Us on the basis of which We will provide You the Services related to Your Flight(s) to the chosen Destination with a Selected Carrier for the Full Price. These Terms & Conditions form an integral part of every Service Agreement.
Terms & Conditions: means Our herein stated terms and conditions.
Website: means the website located at kayak.com including the subdomains for respective markets and/or Our website(s) on which You can make the Booking.

Complete Information. You must provide Us with complete, accurate and correct information and all data necessary for Our provision of the Services to You (especially the information and data (including personal data) necessary for the conclusion of the Contract of Carriage with Selected Carrier(s), for billing and Flight tickets (itinerary, delivery etc.), for which You are requested during the Booking or any time before or after. It is Your responsibility to ensure that all information is correct and updated at the time of the Booking and/or travel. It should also be noted that You must provide all information using Latin script. We are not responsible for any damages, additional cost or any other issues or complications, which may arise as a result of Your failure to provide Us with complete and accurate information.
Intellectual Property. We retain any, and all, rights to Our content we provide to the Website; including software, hardware, products, processes, algorithms, user interfaces, know-how, technologies, designs and other tangible or intangible technical materials or information made available to You by Us throughout the provision of the Services or by using of Our content on the Website. Unless expressly set forth herein, no expressed or implied license or right of any kind is granted to You regarding the Services and/or the Website, or any part thereof, including any right to obtain possession of any source code, data or other technical material relating to the Website. All rights not expressly granted to You herein are reserved to Us. Any work product, developments, inventions, technology or materials provided by Us under these Terms & Conditions and/or the Service Agreement or while using The Website or any Services are exclusively owned by Us. You shall not alter and/or decompile the software used by Us for the provision of the Services and operation of the Website; You shall not make copies of such software. We, in Our sole discretion, may use all comments and suggestions, whether written or oral, provided by You in connection with Your order and use of the Services and or the Website. Furthermore all copyright, trade marks, design rights, database rights, patents and other intellectual property rights (registered and unregistered) in and on the Website belongs to Us and/or third parties. We do not grant You a right or license to use any trade mark, design right, database right, copyright or any other right regarding the content in and on the Website owned or controlled by Us or any other third party except as expressly provided in these Terms & Conditions.
The Trademarks. The trademarks, logos, and service marks (hereinafter referred as the "Trademarks") displayed on the Website are registered and unregistered Trademarks of their respective owners. All Trademarks related to the operating airlines and other third party providers that are displayed on the Website belong to their respective owners and We or KAYAK use these Trademarks solely for Your convenience. Nothing contained on this Website should be construed as Our or KAYAK’s pretension of these third party Trademarks or as granting, by implication, estoppel, or otherwise, any license or right to use any Trademark displayed on the Website without the express written permission of its respective owner, or such third party that may own the Trademarks displayed on the Website. Your misuse of the Trademarks displayed on the Website, or any other content on the Website, is strictly prohibited. You must ensure that Your use of the third party content (Trademarks, logos, watermarks and other registered details) complies with all applicable law and the intellectual property and other rights of the relevant third party provider. You acknowledge and agree that the third party content and services and all intellectual property rights subsisting in the third party content and services will remain the property of the relevant third party provider. No part of the third party content and services may be modified, duplicated, published, uploaded, distributed, translated, adapted, marketed or used, without the prior written consent of the relevant third party provider.

Article 2. Service Agreement

In order to remain in full compliance with all applicable laws and regulations We provide You with all the mandatory information before entering into the Service Agreement with Us:

Service Description. Our Services shall consist of the following:

Displaying the Flights offered and their combination on the Website in cooperation with KAYAK;
Brokerage of the Contract of Carriage between You and the Selected Carrier; and
Delivery of the Flight tickets (itinerary) for the selected Flight(s), which You have purchased in accordance with Art. 1.2.1 hereof, as a result of the Booking, to You in accordance with Art. 2.17 hereof.

Optional Services. Please note that Our Services do not include the services related to the Optional Services, such as the processing of Your request(s) for the Optional Services and We are not obliged to provide You with these Optional Services. However, We may assist You in a reasonable manner with the processing of such request(s) on the basis of separate agreement between You and Us for the flat fee of 20 Euro per request. Please note that the Optional Services may also be subject to additional charges imposed by the Selected Carriers or any other third parties providing the Optional Services.
Means of Distance Communication and Costs. We will not charge You any extra costs in addition to the Full Price for the use of means of distance communication that We use in order to communicate, negotiate and enter into the Service Agreement with You; i.e. there are no service charges for Our communication with You via the Internet or over the telephone. All fees relating to all phone communications with Us are dependent on Your phone provider and We are not liable for any costs incurred and We will not reimburse You for these costs. As such You should request the bill payer’s permission beforehand.
Please note that phone calls between Us and You may be monitored, recorded and stored and we will remind You of this on the call. You hereby acknowledge and agree that Your conversation with Our staff when discussing Your complaint, request or suggestion via telephone may be recorded in the form of an audio recording for the purpose of (i) provision of Our Services under the Service Agreement, (ii) internal inspections of service quality, (iii) improvement of service quality and/or (iv) collecting evidence concerning the transaction implemented via Our customer service department.
Supervisory Authorities. The authorities that supervise Our business activities and to whom You can address complaints are the authorities of the Czech Republic, where our company is established and seated, namely the Czech Trade Inspection Authority [Česká obchodní inspekce], the competent Trade Licensing Office [živnostenský úřad], the Office for Personal Data Protection [Úřad na ochranu osobních údajů], the Office for the Protection of Competition [Úřad pro ochranu hospodářské soutěže]. In the EU it is possible to address Your complaints to the European Consumer Centre Czech Republic ( evropskyspotrebitel.cz/eng ) and the Data Protection Officer of the European Commission.
Service Agreement and Contract of Carriage as two separate legal relationships. You should note that by completion of the Booking with us on the basis of ordering the Flight(s) on the Website You are entering into two separate agreements: (i) the Service Agreement concluded with Us (Please note, you will not enter into any relationships or agreements with KAYAK related to the ordering of the Flight(s)) and (ii) the Contract of Carriage for air transportation concluded with the Selected Carrier(s). These two legal relationships are mutually independent, concluded with different persons, (i) You and Us on one hand and (ii) You and the Selected Carrier on the other, and as such these relationships are regulated by different rules, terms, conditions and usually are governed by different legal orders. The circumstances under which You may withdraw from and/or amend the Service Agreement are explicitly stated in these Terms & Conditions (regarding withdrawal right please see Art. 6.2 hereof). Please note that the stipulation of provision 2.14 regarding exemption from the right for withdrawal from the contract within 14 days from conclusion in accordance to the applicable EU regulation, applies to the Service Agreement concluded between You and Us, because Our business is regulated by the applicable legislation and regulation of the Czech Republic and the European Union. In relation to the potential withdrawal from the Contract of Carriage concluded with the Selected Carrier(s), the terms & conditions of each of the respective Selected Carrier(s) shall apply. By conclusion of the Service Agreement You express and represent to Us that You have the necessary legal capacity to enter into and be bound by these Terms & Conditions and that You are familiar with the terms & conditions of each of the respective Selected Carrier and namely their terms regarding potential withdrawal or termination from the Contract of Carriage, cancellation and change of the Flight(s), and/or any other changes related to the Flight(s).
Storage of the Service Agreements. We store all Service Agreements digitally for Our internal needs. Should You require to see them, please contact Us directly.
Language of the Service Agreement. The Service Agreement is executed in the language selected by You on the Website throughout the Booking. However, please note that only the English version of the herein stated Terms & Conditions is legally binding. Translations have been provided purely for user convenience. In the event of discrepancy between a translation and the English master of the herein stated Terms & Conditions, the English master shall prevail.
Technical Steps to enter into the Service Agreement with Us / Data Correction. The Website contains an interactive web interface through the use of which the Service Agreement between You and Us is concluded by completing and sending Us the online order form and making online payment in accordance with Art. 1.2.1 hereof. Before sending the online order form, You are able to check, change and correct any data You have entered.
Code of Conduct. Throughout the provision of Our Services, We always comply with all applicable laws and regulations of the Czech Republic, United States, European Union and other countries where we provide services and Our internal principles of customer satisfaction and rules for personal data protection. We choose not to make these internal rules and principles public.
Quoted Prices. The prices quoted on the Website include the base fare to the Destination, the airport charges, fuel charges, VAT and fees for Our and KAYAK’s Services. All these components of the quoted price are displayed as a single Full Price. However, given the character of Our Services, Our prices cannot include any extra fees charged by the Selected Carrier, or any other third party in connection with the carriage to the Destination that are not mandatory and/or are not collected at the point of sale. (For more information please see Art. 3.1 hereof).
Territorial Limitations. There are no territorial limitations on the provision of Our Services unless stated otherwise explicitly.
Obligations of the Parties. By concluding the Service Agreement, We undertake to perform Our obligations related to the provision of the Services under these Terms & Conditions and You undertake to pay Us the Full Price in accordance with Art. 3.1 hereof. By completing a Booking, You accept Our offer and enter into the Service Agreement with Us.
Change of Flight(s). We reserve the right to change or cancel any Flights that We offer to You if a Selected Carrier’s offer changes (especially if the change concerns the features of the Flight tickets You have selected). If, during the provision of Our Services, the conditions of carriage are changed by a Selected Carrier, We will notify You accordingly in a reasonable manner and make every effort to offer You reasonable alternative carriage options and proceed in accordance with the provision of Art. 6.2 hereof.
Immediate Performance of the Service Agreement and 14-Days no Withdrawal Period. Given the character of Our Services, which We will start providing immediately after the conclusion of the Service Agreement with You, i.e. before the expiration of the 14-days withdrawal period according to the EU legislation, You shall not withdraw from the Service Agreement within a 14-day period after its conclusion, or at any time thereafter, even if You are a citizen of an EU member state to whom this right generally applies. By concluding the Service Agreement between You and Us, this will be considered Your request for Our immediate provision of Our Services. This provision of Art. 2.14 hereof does not affect the possibility to withdraw from the Service Agreement under the conditions stipulated in Art. 6.2 hereof.
Brokerage of the Contract of Carriage. We are primarily responsible to broker the Contract of Carriage between You and a Selected Carrier. By You making a Booking, You instruct Us to broker a Contract of Carriage between You and a Selected Carrier. The content of any such Contract of Carriage will be determined by Your selection of the Destination and other Flight attributes on the Website and the Selected Carrier’s conditions of carriage. A brokered Contract of Carriage can be applied to carriage of more than one person and/or person(s) other than Yourself; however, the Contract of Carriage is always concluded between You (as the person making the Booking) and the Selected Carrier. The price for the carriage services provided under the Contract of Carriage brokered by Us with the Selected Carrier(s) is included in the Full Price (Art. 3.1 hereof) and does not cover any extra services provided by the Selected Carrier in connection with the carriage to the Destination. Subject to the limitation of Art. 2.13 and 6.2 hereof, We must broker the Contract of Carriage for You without unreasonable delay after We accept Your payment of the Full Price in accordance with Art. 1.2.1 hereof. For this purpose You are entitling Us to act on Your behalf with the Selected Carrier(s). On average We broker Contract(s) of Carriage within 30 minutes unless explicitly stated otherwise. Please note, that the Service Agreement between You and Us and the Contract of Carriage between You and the Selected Carrier(s) are two separate agreements.
Power of Attorney. If the Service(s) is only provided to You on the basis of a power of attorney, You, by entering into the Service Agreement with Us, appoint Us as Your attorney-in-fact and grant Us all such powers to represent You in the extent necessary for the provision of all Services by Us. If a written power-of-attorney is required, You must undertake to provide it to Us upon Our request.
Flight Ticket Delivery. We and/or KAYAK will send You Our e-ticket(s) with the respective PNR for each respective Flight purchased from the Selected Carrier to Your email box at the email address that You entered in the online order form during the Booking on the Website. It is necessary that You enter Your email address in a correct and unabbreviated form. We are not liable for faulty delivery or non-delivery of e-ticket(s) for a Flight, if caused by circumstances on Your part such as entering an incorrect email address or incorrect email settings. You must notify Us of any changes to Your contact information that may affect Our ability to deliver the ordered Flight e-ticket(s) to You. Please be reminded that We do not deliver Flight e-ticket(s) in paper form; please print out the Flight e-ticket(s), boarding pass(es), visa(s), copy of passport and/or other travel documents required by the Selected Carrier(s) and/or relevant authorities and bring them with You to the airport.

Article 3. Fees, Costs and Charges

Full Price. The Full Price that is displayed on the Website is the final price for the Flight ticket(s) and it includes the base fare to the Destination, the airport charges, fuel charges, VAT and price of Our Services. However, it does not include other fees, charges or payments for services related to Your carriage under the Contract of Carriage, which are provided by the Selected Carrier(s) and/or third parties, such as Optional Services, tourist taxes, visa fees, airport transfer fees etc. You must pay the Full Price with a payment card or by another online payment method offered on the Website by entering the required data in the relevant online form on the Website. Until We receive the payment of the Full Price from You and confirm to You its acceptance, We are not obliged to commence the provision of any Service(s).

Article 4. Conditions of Carriage

You acknowledge that a Selected Carrier(s)’s terms and conditions and conditions of carriage will unconditionally apply to Your contractual relationship with the Selected Carrier(s) and that You should make Yourself aware of such terms and conditions as well as conditions of carriage before the Service Agreement is concluded and You complete the Booking, but they will be binding irrespective.
We will provide You with all necessary documents (not including documents that you are responsible for, such as visas, passports, etc.) for Your journey. However, it is Your responsibility to check that all documents have been received and are in order. We are not responsible for any issues arising due to Your failure to ensure that You have all the correct and adequate passport, visa, or other travel documents required by any airline, authority, or the Destination, including countries you may just be transiting through. If You have not received any documentation from Us, or You believe that some of the documentation is missing or inaccurate, You must contact and inform Us immediately and We will make Our best effort to provide You with all the necessary documentation.

Article 5. Administrative Formalities/Governing Laws/Amendments/Fraud

Visas. We are under no obligation to advise You to obtain visas nor assist You in obtaining visas or obtain for You visas to the destinations that You will visit and/or pass through en route to Your Destination. However, We do generally advise You that some of the destinations may require a visa from You and that it is Your responsibility to obtain the required visas early enough, and at Your own expense.
Severability. If any of the provisions of the Service Agreement are found to be invalid or ineffective, the other remaining provisions shall remain fully valid and effective to the extent that they are not dependent on such an invalid or ineffective provision. In such an event, any invalid or ineffective provision shall be replaced with a new, valid and effective one which corresponds to the intent and purpose of the provision that it being replaced.
Governing Law. The Service Agreement and any legal relations established under it or derived from it, including issues of its formation and validity, shall be governed by the laws of the Czech Republic with the exclusion of any rules on conflict of laws.
Personal Data Processing. Our processing and protection of personal data, that You provided to Us, as a natural person in accordance herewith, is governed by Act No. 101/2000 Coll., on the protection of personal data and amendments to some related acts, as amended, as well as by Our Privacy Policy, which is available online on the Website. The Privacy Policy forms an inseparable part of these Terms & Conditions and You are obliged to always read Our Privacy Policy before accepting these Terms & Conditions. By accepting these Terms & Conditions You also confirm that You have read and understood Our Privacy Policy.
Amendments. We reserve the right to amend these Terms & Conditions at any time, and without prior consultation with Our customers. These Terms & Conditions are valid and effective from the time when You send Us a completed online order form via the Website and will apply to the respective Service Agreement. Please be advised that these Terms & Conditions may have changed by the time You choose to use Our Services again, and You should read them carefully before requesting any order of Our Services. All versions of Our Terms & Conditions are available and downloadable on the Website.
Applicability. These Terms & Conditions shall apply to all Service Agreements concluded as of May 1, 2017.
Fraudulent Transaction Protection. To ensure the high standard of Our Services and to protect against fraudulent transactions, We reserve the right to perform checks (verification) of payment cards. For this reason, We may request Your cooperation to verify the identity of the payment card holder. Until successful verification, Our obligation of immediate commencement of the provision of Our Services is suspended. In this event Your funds will be blocked at the bank and therefore We will not withdraw them. The time that it will take to verify a payment card is not included in the period within which We undertake to broker a Contract of Carriage for You in accordance with Art. 2.15. hereof.

Article 6. Discharge / Extinguishment of Obligations

Discharge by Performance. Your and Our obligations under the Service Agreement will be discharged, and the Service Agreement performed, when You pay the Full Price in accordance with Art. 3.1 hereof and We provide the Services to You.
Extinguishment by Default. We continuously update Our offers for Flights in order to provide You with the most up to date Flight information, however, from time to time the Flights may not be available anymore or the Flights prices may change. If We fail to broker the Contract of Carriage for You in accordance with Art. 2.15 within a reasonable time after We accept Your payment of the Full Price and not later than 48 hours, We will contact You. We will try to offer You an alternative solution, or either You or Us may withdraw from the Service Agreement. If You or We withdraw from the Service Agreement, You will be entitled to a refund of the Full Price in accordance with Art. 6.3 hereof. If we agree on an alternate Flight or another combination of Flights to Your Destination, the Full Price may change. You and Us will settle the price difference between the original Full Price and the new Full Price. Such price differences will be payable either by You to Us or vice versa based on Our calculation provided to You.
Refund process. If You are, under these Terms & Conditions, entitled to receive a refund of the full or partial price You originally paid Us or another form of refund, it will be refunded to the payment card account that You used to pay Us the Full Price. This can take up to 10 working days; if it is not possible, the refund will be provided by a method mutually agreed between You and Us within 14 days after We reach such an agreement on the method of refund. It is pertinent to mention that We bear no responsibility in relation to the money, because We cannot anyhow influence the transfer process of the refund and that responsibility solely lies with the financial institutions responsible for remitting the transaction from Us to You.

Article 7. Liability for Damage

We and KAYAK are not liable for any damage, harm or loss arising out of any actions or omissions of a Selected Carrier or other third parties in connection with carriage to the Destination. Neither are We liable for any damage, harm or loss arising out of Your actions or omissions that are contrary to these Terms & Conditions.

Article 8. Dispute Resolution

In Brno on 1 May, 2017.

Flights from Prague (Czechia)‎ to Montego Bay (Jamaica)‎

Một chiều tốt nhất

Khứ hồi tốt nhất