Definition: 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
Input: customer: Hi. 
 agent: Hello, how can I help you? 
 customer: I am Elizabeth Gonzalez. I am looking for a direct flight from IAH to DTW, please book my flight ticket. 
 agent: May I know your desired travel dates please? 
 customer: Sure, I want to depart on Dec 4th and I have to return back in the afternoon on Dec 6th. 
 agent: Please wait a while. 
 customer: Sure. 
 agent: There is a flight with connection limit 1 and fare 200, shall I proceed for booking? 
 customer: No, I prefer for a direct flight. 
 agent: Sorry to say, there is no flight available on your desired travel dates. 
 customer: Sad to hear that, thank you for checking. 
 agent: Thank you for opting us.
Output:
no_flight