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: Can you help me to book a flight ticket from PHX to ATL? 
 agent: May I know your desired travel dates please? 
 customer: Ok, please can you book a flight ticket for the dates Dec 15 and Dec 17 respectively? 
 agent: Do you prefer a direct flight or connecting flight? 
 customer: Ok, please book a connecting flight. 
 agent: May I know your name please? 
 customer: My name is Mary Miller. 
 agent: There is a flight with connection limit 1 and fare 100, shall I proceed for booking? 
 customer: Yes, please book. 
 agent: Your ticket is booked, flight number 1004 with Spirit Airlines. 
 customer: Ok, that is good to know. Thank you for assisting me. 
 agent: Thank you for opting us.
book