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,. 
 agent: Hello. How can I aid you? 
 customer: I need a ticket from Las Vegas, NV-LAS to Washington DC-DCA. 
 agent: Sure, I  can help you. Please share me your travelling dates. 
 customer: Departure date is 10/26 and 10/28 is my return date. 
 agent: Do you need any connecting flight? 
 customer: I need direct flight. 
 agent: May I know your name? 
 customer: I am Emily Young. 
 agent: Unfortunately, there are no flights found according to your specifications. 
 customer: Thanks. 
 agent: Thank you for choosing us.
no_flight