You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I serve you?

USER: I am looking to book a flight ticket from AUS to DCA. Can you help me for that?

ASSISTANT: Sure, I will help you. Please send your travelling dates on which you like to start and return back.

USER: My travelling dates are Apr 25 and Apr 27.

ASSISTANT: Do you have any preferences?

USER: No.

ASSISTANT: May I know your name please?

USER: My name is Susan Robinson.

ASSISTANT: Sorry, there is no flight available with your requested dates.

USER: That's ok, thank you for checking.

ASSISTANT: You are welcome, have a nice day.