You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, do you need any help from us?

USER: I am planning to book a ticket from DCA to DEN. Can you please help me out?

ASSISTANT: Sure, can you please tell me your trip dates?

USER: I am planning to travel on Aug 13 and return back Aug 15.

ASSISTANT: Ok, could I have your name please?

USER: My name is Kathleen Allen.

ASSISTANT: Ok, do you need direct or connecting flight?

USER: I am looking for a connecting flight.

ASSISTANT: Ok, do you have any other specifications?

USER: My return time should be evening.

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

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

ASSISTANT: You are welcome.