You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you?

USER: I am Jeffery Brown. I have to book a flight ticket  that I am unable to do, could you please help me in booking flight ticket on dates 12/28 and 12/30?

ASSISTANT: Sure, may I know your source and destination airport codes please?

USER: Yes, my airport codes are CO-DEN and DC-IAD.

ASSISTANT: Please wait for a moment.

USER:   Ok.

ASSISTANT: Sorry, there is no flight available on your requested dates.

USER: That's ok, thank you for the response.

ASSISTANT: You are most welcome.