You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. What kind of help are you expecting from my side?

USER: I'm Sandra Lewis. I am planning to travels from DCA to DFW for a business meeting, can you please help me with booking a flight ticket?

ASSISTANT: Yes, I can help you with that. Is there any preferable dates for you?

USER: Sure, I would like to take off on 12/18 and return back on 12/20.

ASSISTANT: Sorry to say you that there are no flights available which matches with your preferences.

USER: Ok, no issues. I will search for another way to complete my trip. Thank you for checking.

ASSISTANT: Thank you, have a wonderful day.

USER: You are welcome.