You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: I am Carol Hill. I would like to book a flight ticket from HOU to LAS, can you please help me to book  flight ticket?

ASSISTANT: May I know your desired travel dates please?

USER: Sure, my journey dates are from 09/20 to 09/22.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: That's ok, no problem. Thank you for your help.

ASSISTANT: Thank you for opting us.