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, myself Elizabeth Clark. 
 agent: Hello, how can I assist you? 
 customer: Can you please help me in booking a flight ticket from MSP to DCA? 
 agent: Sure, may I know your preferred dates of travel? 
 customer: My preferable travel dates are from May 15th to May 17th. 
 agent: Is there any class preference? 
 customer: No. 
 agent: Do you have any specifications? 
 customer: I want to return in the afternoon. I want a stopover in between my journey. 
 agent: Ok, please wait a minute. 
 customer: Ok. 
 agent: Sorry, there were no flights found on your route. 
 customer: Ok, no problem. Thank you. 
 agent: Thank you.
no_flight