Given the task definition and input, reply with output. 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. 
 agent: Hello. How may I aid you today? 
 customer: I want to change my existing reservation, as my exams has postponed. Can you please help me with this? 
 agent: Sure, I am oblige to help you. Can you please provide your name to check your previous reservation? 
 customer: I am Sharon Nelson. 
 agent: Ok, please be on hold. We regret that, there is no reservation found with your name in our records. 
 customer: Ok, no problem. 
 agent: Thank you for reaching us, have a great day. 
 customer: Thank you for your information. 
 agent: Most welcome.
no_reservation