You will be given a definition of a task first, then some input of the task.
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, I am Dorothy Evans. 
 agent: Hello,. How may I help you? 
 customer: I want to change my reservation, can you help me with it? 
 agent: Please wait for a while. 
 customer: OK. 
 agent: No reservation exists. Thanks.
Output:
no_reservation