Given the task definition and input, reply with output. 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

customer: Hello. 
 agent: Hello, how can I help you? 
 customer: I am Nicole Robinson. I am planning to watch movie in Broadway theatre at New York, JFK with my friend. Can you please book a ticket on 04/20? 
 agent: Sure, can you please share your return date? 
 customer: I will return on 04/22. 
 agent: May I know your origin airport code? 
 customer: Source code is Charlotte, CLT. 
 agent: Please wait for a while. 
 customer: Sure. 
 agent: Sorry, no flights found on your given dates. 
 customer: No problem. Thank you. 
 agent: Thank you for choosing us.
no_flight