You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I aid you?

USER: I have to go PHL for my film shooting purpose, can you please book a flight ticket from Denver?

ASSISTANT: Yes, I am gleeful to assist you.

USER: Thanks.

ASSISTANT: May I know your travelling trip dates?

USER: My departure date 10/22 and please book my return ticket also on 10/24.

ASSISTANT: Please provide your source region code.

USER: My source airport code is DEN.

ASSISTANT: May I know your name?

USER: Sure, my name is Christopher Smith.

ASSISTANT: I am sorry that, I am unable to find a flight on the trip dates that you have given. Sorry for the trouble.

USER: Oh! It's ok no problem, I will go with another airline. Thank you for your information.

ASSISTANT: Thank you for reaching us. Most welcome.