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 aid you? 
 customer: My name is William Lopez. Actually, I booked a ticket to NYC for a music concert but due to bad weather the trip is cancelled. 
 agent: Ok, so would you like me to change your existing reservation? 
 customer: Yes, help me out. 
 agent: Ok, please hold on for a moment. 
 customer: Sure, take your time. 
 agent: Sorry, I could not find any ticket booked with your name. 
 customer: That's ok. Thank you for your time. 
 agent: Thank you, have a great day.
no_reservation