You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Gregory Lopez. I am planning to book a ticket from ATL to LAS. Can you please help me out?

ASSISTANT: May I know your desired travel dates please?

USER: I would like to travel on 04/20 and return back on 04/22.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for opting us.