You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how can I aid you?

USER: Please book a ticket from Las Vegas, NV-LAS to San Francisco, CA-SFO.

ASSISTANT: Sure, please let me now your travelling dates.

USER: Travelling dates are from 12/01 to 12/03.

ASSISTANT: May I have your name please?

USER: I am David Anderson.

ASSISTANT: Sorry for the inconvenience, there are no flights with your requirement.

USER: Thank you.

ASSISTANT: Have a good day.