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: Please help me to book a flight from ORD to SFO. 
 agent: Can I know your journey dates? 
 customer: Sure, I want to travel on Nov 19 and need to return on Nov 21. 
 agent: Do you need connecting flight? 
 customer: I need a direct flight. 
 agent: Is there any class preference? 
 customer: No. 
 agent: Please let me know your name? 
 customer: My name is Paul Collins. 
 agent: Sorry currently there is no flight for your travelling dates. 
 customer: Ok, no problem. 
 agent: Thank you. 
 customer: Thank you for checking.
no_flight