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 assist you today? 
 customer: Edward Young here. I would like to change my recent reservation, can you help me? 
 agent: Ok, let me check with your existing reservation for a moment. 
 customer: Sure. 
 agent: Thank you for waiting. 
 customer: It's ok. 
 agent: I'm so sorry to inform you, there is no reservation found by your name in our data base. 
 customer: That's fine, anyway thanks for your help and valuable information. 
 agent: Thank you for approaching our agency.
no_reservation