You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am Melissa Garcia. I want book a flight ticket from IAD to DEN.

ASSISTANT: Sure, can I know your preferable dates?

USER: I am planning to start on 07/15 and return back on 07/17.

ASSISTANT: I am sorry, there are no flights.

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

ASSISTANT: Thank you, have a good day.