You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Davis.

ASSISTANT: How may I help you?

USER: I want to go to Phoenix, can you help me to book a ticket with price under 500?

ASSISTANT: Sure, I will help you out. May I know you travelling dates please?

USER: My travelling dates are 10/20 to 10/22.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: May I know your airport codes please?

USER: I planned to start from BOS to PHX.

ASSISTANT: Ok, please wait moment.

USER: I need a direct flight. Sure.

ASSISTANT: Sorry, there are no flights found.

USER: No issue, thank you.

ASSISTANT: Thank you for choosing us.