You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Nancy Roberts here.

ASSISTANT: How can I assist you?

USER: Can you book a flight ticket for my airport codes that is from IAH to DEN?

ASSISTANT: Sure, can I know the travel dates please?

USER: My preferable dates for travel would be from Dec 20 to Dec 22.

ASSISTANT: Ok, wait a moment please.

USER: Sure.

ASSISTANT: Sorry, there are no flight found on your dates.

USER: Ok, not a problem.

ASSISTANT: Thank you for approaching us.

USER: Thank you.