You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am William Anderson.

ASSISTANT: William, how can I aid you today?

USER: Can you please help me to book a flight ticket from PHX to LAX?

ASSISTANT: Sure, I am here to help you. May I know your travel dates please?

USER: Thank you. My travelling dates are Apr 28 to Apr 30.

ASSISTANT: Ok, hold on for a moment. Let me check the best flight for you.

USER: Sure.

ASSISTANT: Sorry William, there are no flights available on your requested dates.

USER: No problem, thanks for your information.

ASSISTANT: Welcome, thank you for choosing us. Have a safe flight.