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. 
 customer: I am Mary Smith. 
 agent: How can I assist you? 
 customer: I am going to Houston, TX-HOU to purchase a vintage car from a dealer. Can you hold me a ticket? 
 agent: Sure, may I know your source airport code please? 
 customer: My source airport code is Atlanta, GA-ATL. 
 agent: Please provide the travel dates. 
 customer: My travelling dates are from 11/24 to 11/26. 
 agent: Frontier airlines is having a flight on that route with travel charge of 200, shall I proceed for booking? 
 customer: Please proceed for booking. 
 agent: Your ticket has been booked with flight-1002, have a safe journey. 
 customer: Thanks for your help. 
 agent: Thank you for choosing us.
book