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 may I guide you? 
 customer: I am Christine Smith. I would to book a flight ticket from OAK to DEN. 
 agent: Sure, can I know your preferable dates? 
 customer: I am planning to start on 12/15 and return back on 12/17. 
 agent:  I found a flight 1011 of AA airlines matches with your preferences, can I proceed? 
 customer: Yes, please proceed. 
 agent: Your ticket is booked. 
 customer: Thank you. 
 agent: Thank you, have a good day.
book