Detailed Instructions: 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
Problem:customer: Hello. 
 agent: Hello. How can I help you today? 
 customer: My name is Michelle Green, I just need your help in changing my existing reservation details. 
 agent: Sure, please wait for a while. 
 customer: Ok. 
 agent:  I haven't found your previous reservation in our portal to change further. 
 customer: That's ok, thank you for the information. 
 agent: Thank you for opting us.
Solution:
no_reservation