You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I want to book a flight from OAK to IAD. Can you please help me with the booking?

ASSISTANT: Sure, may I know your trip dates please?

USER: Sure, I want to travel on Dec 10 and need to return on Dec 12.

ASSISTANT: Do you have any other requirements?

USER: Yes, I need a direct flight with business class.

ASSISTANT: Ok, can I know your name please?

USER: Sure, my name is Cynthia Carter.

ASSISTANT: Sorry, we regret to inform you that there is no flight available as per your request.

USER: Ok, not an issue. Thank you for checking.

ASSISTANT: Most welcome.