You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I serve you the best today?

USER: I want to book a ticket from DEN to LAS. Could you book a ticket?

ASSISTANT: Sure, can I know your good name please?

USER: My name is Daniel Green.

ASSISTANT:  When you are willing to travel?

USER: Depart date is May, 29 and return by May, 31.

ASSISTANT: Do you need direct flight or connecting flight?

USER: I would prefer connecting flight.

ASSISTANT:  Would you let us know if you have any other preferences?

USER: I prefer business class.

ASSISTANT: Sorry to say that, there are no flights available on the routes of your journey.

USER: Thank you.

ASSISTANT: Thank you for opting us.