Teacher: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
Teacher: Now, understand the problem? Solve this instance: customer: Hi. 
 agent: Hello, how can I aid you? 
 customer: Could you please change my existing reservation due to postpone of my exams? 
 agent: Sure, may I know your name to proceed further? 
 customer: My name is Donna Adams. 
 agent: We regret to inform you that there is no active reservation found on your name to change. 
 customer: Not a problem, thank you. 
 agent: Thank you for contacting us.
Student:
no_reservation