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, What kind of help are you expecting from our side? 
 customer: I want to change my existing reservation due to postpone of my event. Can you please help me? 
 agent: Sure, I can change your reservation right now. Before that I need to know your good name please? 
 customer: I am Barbara Carter. 
 agent: Ok, wait for some time I will check the reservation on your name and get back to you. 
 customer: Sure. 
 agent: Thanks for remaining so positive, We are sorry to specify that there is no active reservation found on your name. 
 customer: No worries, thank you for the information. 
 agent: Thanks for approaching us, wish you a nice day.
no_reservation