You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Barbara Martinez. I would like to travel from Washington to Denver on a business trip. Will you please help me to get a flight ticket?

ASSISTANT: Sure, if you know your airport codes then please tell me once.

USER: Sure. Airport codes are DC-DCA to CO-DEN.

ASSISTANT: Your trip dates please.

USER: My trip dates are 12/11 and 12/13.

ASSISTANT: Sorry Barbara Martinez, I don't found any flight. Thank you to join us.