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 serve you? 
 customer: Could you book my ticket in a connecting flight? 
 agent: Sure, help me with the trip dates? 
 customer: My trip dates are July 19 and July 21. 
 agent: May I know your airport codes that you wish to board and land? 
 customer: I want to travel from ATL to ORD. 
 agent: Do you have any class preferences? 
 customer: I prefer economy class. 
 agent: May I know your name please? 
 customer: Sandra Green here. 
 agent: We found a flight in an airline Delta with 1004 number having a single connection price of 200 in an economy class. Shall I reserve it? 
 customer: Please book my ticket. 
 agent: Your flight ticket has been booked. 
 customer: Thank you. 
 agent: Thank you for reaching us.
book