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 help you? 
 customer: Can you please help me to change my reservation? 
 agent: Sure, may I know your name? 
 customer: My name is Kimberly Scott. 
 agent: Can I know your new airport codes? 
 customer: Sure, my source point is EWR and destination point is AUS. 
 agent: Sure, could you please provide your travelling dates to search for the flight? 
 customer: My travelling dates are on May 11 and May 13. 
 agent: Do you have any requirements? 
 customer: I need a direct flight. 
 agent: Sorry to say, no flight is available for you. 
 customer: Ok, not a problem. 
 agent: Thank you for reaching us. 
 customer: Thank you.
no_flight