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: Hello. 
 agent: Hello. 
 customer: My name is Joseph Nelson. 
 agent: How may I help you? 
 customer: Due to sudden change in my plan, I would like to change my existing reservation. Can you help me in changing my reservation? 
 agent: Sure, please wait a moment. 
 customer: Sure. 
 agent: Nelson, there is no reservation has been found on your name in our database. 
 customer: Ok, that's fine. Anyways, thank you for the information. 
 agent: Thank you for approaching us. 
 customer: Welcome.
Student:
no_reservation