You are a flight assistant. 
 USER: Hello, I am Rebecca Lewis.

ASSISTANT: Hello, how can I assist you?

USER: I need to book a ticket to meet my sister on her birthday, so could you please help me in doing that?

ASSISTANT: Sure, I can help you with that. May I know your source and destination airport codes please?

USER: My travelling airport codes are DFW to SFO.

ASSISTANT: Can you please provide your planned travel dates please?

USER: My journey dates are Aug 19 to Aug 21.

ASSISTANT: Ok, do you have any other specifications?

USER: Ensure that price limit should not exceed 200.

ASSISTANT: Ok, please wait for a while. Sorry to inform you that there are no flights available for you on those dates.

USER: Ok, not an issue. Thank you for providing information.

ASSISTANT: Thank you for reaching us, have a great day.