You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I want to book a flight ticket from IAD to IAH. Could you help me in booking?

ASSISTANT: May I know your desired travel dates please?

USER: My travelling dates are from Sep 28-30.

ASSISTANT: Do you have any specifications?

USER: I need direct flight and my return time should be in the afternoon.

ASSISTANT: May I know your name please?

USER: Ryan King here.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: That's ok, no problem. Thank you.

ASSISTANT: Thank you for opting us.