Teacher: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
Teacher: Now, understand the problem? Solve this instance: customer: Hello. 
 agent: Hello, how may I help you? 
 customer: This is Richard Scott, can you help me to book a flight ticket from DTW to IAD? 
 agent: Sure, could you please provide your travelling dates to search for the flight? 
 customer: I am travelling from Sept 14 to Sept 16. 
 agent: Please wait for a moment. 
 customer: Sure. 
 agent: Sorry to say, no flight is available for you. 
 customer: That's ok, no issues. 
 agent: Thank you for reaching us, have a nice day. 
 customer: Thank you for the information.
Student:
no_flight