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, I am Alexander Scott. 
 agent: Hello, how can I assist you? 
 customer: I need to alter my reservation, as my exam scheduled has been postponed. Please help me in changing? 
 agent: Sure, please wait a moment. 
 customer: Ok. 
 agent: Sorry, there is no reservation found on your name. 
 customer: Ok, no worries. Thanks for your help. 
 agent: Thank  you for choosing us.
no_reservation