You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Lisa Nelson here. I have planned to enjoy weekend in Denver. So please help me to get a flight ticket.

ASSISTANT: That's great to hear. Will you provide your source and destination airport codes.

USER: My airports codes are NC-CLT and CO-DEN.

ASSISTANT: Can you provide your travelling dates?

USER: Sure, my travel dates are 04/19 and 04/21.

ASSISTANT: OK, please give me a moment.

USER: Sure.

ASSISTANT: Thanks for waiting. Sorry to say that Lisa, there is no flights found under your requirements.

USER: Oh!. That's fine. Thank you for your help.

ASSISTANT: Thanks for reaching us. Have a nice day.