You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: Can you please book a flight from DCA to DEN?

ASSISTANT: Provide me with the travel dates please.

USER: Sure, I intend to depart on Sept 11 and need to return on Sept 13.

ASSISTANT: Is there any class preference?

USER: I want an business class.

ASSISTANT: May I know the connection limit.

USER: Yes, I need a connecting flight.

ASSISTANT: Are there any more preferences?

USER: No.

ASSISTANT: May I know your name please?

USER: My name is Timothy Young.

ASSISTANT: Sorry to inform that there are no flights on your route with the given dates.

USER: Ok, no problem. Thank you for checking.

ASSISTANT: Thank you for reaching us.