You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Timothy White here.

ASSISTANT: How can I assist you?

USER: I need to book a flight ticket, can you please help me in that?

ASSISTANT: Sure, can you please mention your airport codes?

USER: My preferable travelling airline code are from IAD to LAX.

ASSISTANT: Ok, can you please give your trip dates?

USER: I want to travel on 12/20 and return back on 12/28.

ASSISTANT: Ok, please be on hold.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry, for the inconvenience there are no flights available on this route.

USER: Its ok, no problem. Thank you for your help.

ASSISTANT: Thank you for contacting our agency.