You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Can you please help me to search a flight from Las Vegas, NV-LAS?

ASSISTANT: Sure, may I know your destination code?

USER: The destination code is DC-IAD.

ASSISTANT: Can you please tell me your travel dates?

USER: The travel dates are 02/18 to 02/20.

ASSISTANT: May I know your name?

USER: Sure, my name is Ronald Lee.

ASSISTANT: Sorry, I didn't find any flight for you.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you for opting us.