You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am David Green.

ASSISTANT: How may I help you out?

USER: I am planning to travel from ORD to DEN to enjoy the fun filled vacations. Can you please reserve me a flight ticket?

ASSISTANT: Sure, I will help you in booking the ticket. May I know your travelling dates please?

USER: I would like to depart on Oct 29 and return on Oct 31.

ASSISTANT: Do you have any connection limit?

USER: I need a flight with single connection.

ASSISTANT: Do you have any class preferences?

USER: I am comfortable with any class.

ASSISTANT: Do you have any other specifications?

USER: My depart time should be evening.

ASSISTANT: Sorry, there are no flights found.

USER: Ok, no problem. Thank you for the information.

ASSISTANT: Thank you for reaching us.