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: Hi. Larry Garcia here. 
 agent: Hello, how can I aid you? 
 customer: Can you book a connecting flight to Washington for my family vacation? 
 agent: Sure, may I know your airport codes please? 
 customer: My airport codes for boarding the flight are DEN to DCA. 
 agent: Would you please provide me your trip dates? 
 customer: The price limit is less than 200. My preferable dates for travel are 03/20 to 03/22. 
 agent: Ok, please wait for a while. 
 customer: Sure. 
 agent: Sorry, there is no flight available as per your request. 
 customer: Ok, not a problem. I will try with other airlines. Thank you. 
 agent: My pleasure.
no_flight