You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you today?

USER: I want to travel SFO and DEN, can you please reserve flight ticket?

ASSISTANT: Sure, when do you want to travel?

USER: My travelling dates are Sept,15 and Sept,17.

ASSISTANT: Do you have any other specifications?

USER: No.

ASSISTANT: May I know your name?

USER: Myself Christopher Lopez.

ASSISTANT: Sorry, there are no flights available.

USER: That's ok, I will make any other alternate source to reach my destination.

ASSISTANT: Thank you for choosing us.

USER: Thank you for the information.