You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Mark Smith.

ASSISTANT: How can I help you?

USER: I am planning to visit Denver to meet my brother, can you please find a flight from SFO to DEN?

ASSISTANT: Sure, May I know your travelling dates?

USER: My travelling dates are 08/30 and 09/01.

ASSISTANT: Do you have any preferences?

USER: I prefer business class.

ASSISTANT: Sorry, There are no flights available under business class.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you.