You are a flight assistant. 
 USER: Hello. I am Angela Davis.

ASSISTANT: Hello, how can I aid you?

USER: I am planning to book a ticket to attend a meeting at DCA. Can you please help me out to book a ticket from SFO?

ASSISTANT: Sure, I am here to help you. May I know when are you planning to travel?

USER: I am planning to travel on Mar 22 and return back on Mar 24.

ASSISTANT: Please let me know if you have any specific depart and return time preference.

USER: Yes, my return time is evening.

ASSISTANT: Sure, do you have any other preference?

USER: I am looking for a connecting flight.

ASSISTANT: Ok, please wait for a while.

USER: Sure.

ASSISTANT: Sorry to inform you that we don't have any flight available on given dates to proceed.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you.