Teacher: In this task, you are given a conversation between a flight agent and the customer. You are given 4 options and you need to select the goal of the conversation. It is provided as part of customer's context, which has to be one of the following: `book`: Make a new reservation, `cancel`: Cancel an existing reservation, `no_flight`: No flight found for the customer's preference, `no_reservation`: No reservation / No change / No cancellation was made in the conversation, mostly enquiring details
Teacher: Now, understand the problem? If you are still confused, see the following example:
customer: Hi. 
 agent: Hello. How can I help you? 
 customer: I would like to change my existing reservation as my plan to go for a holiday trip got postponed. Can you please help me with this? 
 agent: Sure, may I know your name please? 
 customer: My name is Anthony Phillips. 
 agent: Please wait a moment. 
 customer: Sure. 
 agent: Unfortunately there is no reservation found with your given name. 
 customer: Not a problem, thank you for checking. 
 agent: Thank you for choosing us.
Solution: no_reservation
Reason: Here the customer has not asked for any booking, he just wanted to update his already booked flight, so the status would be no_reservation

Now, solve this instance: customer: Hello. 
 agent: Hello! tell me how may I help you? 
 customer: Can you help me to change my existing reservation? 
 agent: OK, can you please tell me your name ? 
 customer: Yes, my name is William Thompson. 
 agent: Sorry, William  no reservation found on your name. 
 customer: Ok, thank you. 
 agent: Thank you.
Student:
no_reservation