You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you?

USER: I need your help to book a flight ticket on 11/18 and 11/20.

ASSISTANT: OK, may I know your origin and destination airport codes?

USER: Sure, my origin code is NC-CLT and destination code is CA-SFO.

ASSISTANT: Sorry, unfortunately there is no flight in these travel dates.

USER: OK, that's fine.

ASSISTANT: May I know your name please?

USER: Sure, I am John Thomas. Thank you.

ASSISTANT: Thank you, have a good day.