You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Gregory Evans. I would like to book a flight ticket which departs in the afternoon. Could you please help me with booking a flight ticket?

ASSISTANT: Sure, I can do that for you. Can you please let me know your travel dates?

USER: Sure, my travelling dates are Dec 17 and Dec 19.

ASSISTANT: Ok, please provide us your source and destination airport codes.

USER: Sure, my airport codes are DEN and AUS.

ASSISTANT: Ok, do you have any class preference?

USER: I am comfortable with any class.

ASSISTANT: Ok, please wait for a while.

USER: Sure.

ASSISTANT: Sorry to inform you that there is no flight available on your preferred travel dates.

USER: No worries, thank you for the information.

ASSISTANT: You are welcome and thank you for choosing us.