You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Please book a ticket from Las Vegas, LAS to attend Science festival. Can you please help me for booking?

ASSISTANT: Sure, please provide your trip dates.

USER: My trip dates are Mar 20 and Mar 22.

ASSISTANT: Do you have any other requirements?

USER: My depart time is evening.

ASSISTANT: May I know your name?

USER: Sure, I am John Hall.

ASSISTANT: Sure. Ok, please wait a minute.

USER: Ok.

ASSISTANT: Sorry John, there is no flight available.

USER: Ok, no issues. Thank you.

ASSISTANT: Most welcome.