You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Jack Williams here, please book my round trip ticket from SFO.

ASSISTANT: Sure, may I know your trip dates?

USER: My trip dates are from 12/01 to 12/03.

ASSISTANT: Sorry, there is no flights available.

USER: That's fine. Thank you.

ASSISTANT: Welcome.