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, I am Stephen Collins. 
 agent: Hello, How can I assist you? 
 customer: I would like to attend a seminar on social issues in pioneer plaza at Dallas & Fort Worth, DFW. Can you please help me with it? 
 agent: Sure, May I know the source code? 
 customer: Source code is SFO. 
 agent: Please help me with your travel dates. 
 customer: Travel dates are 07/19 and 07/21. 
 agent: Please wait a minute. 
 customer: OK. 
 agent:  Thanks for sharing your details, we are unable to provide flight in between your journey routes due to heavy snowfall at destination airport. 
 customer: Ok, no issues. 
 agent: Thank you for reaching us. 
 customer: Thanks for the help.

no_flight