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: Hi. 
 agent: Hello, how may I help you today? 
 customer: I have to change my existing reservation, can you please help me? 
 agent: Sure, we are perky to help you. 
 customer: Thank you. 
 agent: May I know your good name? 
 customer: Sure, my name is Stephen Lee here. 
 agent: Please be on hold. 
 customer: Sure, I will wait. 
 agent: There is no reservation found on your name in our database to change it. 
 customer: Ok, not an issue.Thank you for your information. 
 agent: Thank you.
no_reservation