You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Helen Evans, want to travel from DCA to HOU. Please help me in ticket booking.

ASSISTANT: Sure, may I know your trip dates please?

USER: My travel dates are from 09/12 to 09/14.

ASSISTANT: Please wait of a while.

USER: Ok.

ASSISTANT: Sure, there is no flight available as per your request.

USER: That's fine, thank you.

ASSISTANT: Most welcome.