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: Hi. 
 agent: Hello, how may I help you? 
 customer: Can you book a ticket for me with my name Elizabeth Green? 
 agent: Sure, may I know airport codes? 
 customer: Thank you, my preferable locations are from PHX to DTW. 
 agent: May I know your trip dates? 
 customer: Sure, my planned dates are from 11/29 and 12/01. 
 agent: There is a flight for you with 1 connection. Shall I proceed? 
 customer: Please proceed. 
 agent: Your ticker is booked. 
 customer: Thanks for your response and great service. 
 agent: Most welcome.
book