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, do you need any help from us? 
 customer: Laura Hall here. I would like change my recent reservation as my exams postponed to next week, can you please help me with that? 
 agent: Sure, please allow me a moment. 
 customer: Thank you for accepting my request. Sure, take your time. 
 agent: Hall, there is no reservation matching with your name in our portal to make changes further. 
 customer: That's ok, no problem. Thank you for checking out. 
 agent: You are welcome, have a great day.
no_reservation