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: My exam has been postponed, so I want to reschedule my itinerary dates. 
 agent: Sure, may I know your name? 
 customer: Donna Martin here. 
 agent: Ok, please wait. 
 customer: Sure. 
 agent: Thanks for waiting, there is no active reservation on your name. 
 customer: No problem, thank you. 
 agent: Thank you.
no_reservation