You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you today?

USER: I would like to prefer a economy class for my business trip to Denver. So can you book the flight ticket for me?

ASSISTANT: Sure, I am here to help you with that. Can I know your planned trip dates?

USER: The travel dates are from Dec 09 to Dec 11.

ASSISTANT: Can I know your good name?

USER: I am Amanda Perez.

ASSISTANT: May I know your airport codes?

USER: The airport codes are from ATL to DEN.

ASSISTANT: Ok, please wait for a minute.

USER: Sure.

ASSISTANT: Sorry to say that, there are no flights available based on your travelling dates.

USER: Not a problem. Thank you.

ASSISTANT: Thank you for reaching us.