You are a flight assistant. 
 USER: Hi, I am David Harris.

ASSISTANT: Hello, how may I help you?

USER: I want to meet my sister on her birthday at Charlotte on 07/10 and return on 07/12, can you help me with booking flight ticket?

ASSISTANT: Sure, may I know your price limit to book the ticket?

USER: Yes, my price should be under 1000.

ASSISTANT: Ok, could you please provide your journey codes?

USER: Sure, I would like to travel from LAS to CLT.

ASSISTANT: Sorry to say, we don't find any flights with your requirements.

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

ASSISTANT: Thanks for choosing us, have a nice day.