You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Sarah Thomas. I need a direct flight which is travelling from HOU to DCA. Please help me in booking my ticket.

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

USER: Sure, my trip dates are from 01/11 to 01/13.

ASSISTANT: I am really sorry but on these dates, no flights are available.

USER: It's ok, thank you for your help.

ASSISTANT: Most welcome.