You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. What help that you need form us?

USER: I'm Patrick Moore. I am planning to attend music concert at Washington, can you please help me with booking a flight ticket?

ASSISTANT: Sure, I can help you. Can you please help me in providing your preferable travelling dates?

USER: Sure, I would like to take off on 03/20 and return back on 03/22.

ASSISTANT: Can you please help me in providing your regional airport codes?

USER: My source airport code is MCO and the destination airport code is DCA.

ASSISTANT: Let me check with it, please give me a moment.

USER: Ok, but please make sure that the price limit does not exceed 500.

ASSISTANT: Sorry to say that Patrick Moore, no flight is obtained when I when I checked.

USER: Ok, no issues. Thank you for the information.

ASSISTANT: It's my pleasure.