You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I assist you today?

USER: Could you help me in booking a flight ticket from DFW to SFO?

ASSISTANT: Sure, I can help you with that. May I know your planned travel dates please?

USER: I want to fly on Dec 18, return on Dec 20.

ASSISTANT: Do you prefer stopover in between your journey?

USER: I need a connecting flight.

ASSISTANT: Please let me know if you have any other specifications.

USER: My depart time should be evening.

ASSISTANT: May I know your good name please?

USER: My name is Shirley Green.

ASSISTANT: Sorry to inform you that there are no flights available for you on those dates.

USER: Not an issue, thank you.

ASSISTANT: Thank you for choosing us, have a nice day.