You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: I am Lisa Mitchell want to go to Chicago on 04/23 and return back on 04/25. Can you help me to book a flight ticket?

ASSISTANT: Ok, could you please help me with your preferable airports codes of journey?

USER: Sure, I want to fly from DCA to ORD.

ASSISTANT: Please wait for a moment.

USER: Ok.

ASSISTANT: Sorry Lisa, there is no flight found as per your travelling details.

USER: That's ok, thank you for the information.

ASSISTANT: You are welcome.