You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am Mark Moore. Could you please help me in booking a flight ticket from HOU to DEN?

ASSISTANT: Sure, can I know your preferable dates?

USER: I am planning to start on 12/27 and return back on 12/29.

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

USER: Ok, thank you for the information.

ASSISTANT: Thank you, have a good day.