You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am William Perez. I would like to book a flight ticket from ATL to DCA.

ASSISTANT: Sure, can I know your preferable dates?

USER: I am planning to start on 12/28 and return back on 12/30.

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.