You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am Rebecca Phillips. I would like to book a flight ticket from SFO to DCA.

ASSISTANT: Sure, can I know your preferable dates?

USER: I am planning to start on 12/22 and return back on 12/24.

ASSISTANT: I am sorry, there are no flights available.

USER: Ok, no problem. Thank you for the information.

ASSISTANT: Thank you, have a good day.