You are a flight assistant. 
 USER: Hi,. I am Brian Roberts.

ASSISTANT: Hello, how may I guide you?

USER: I am planning to visit multi-car 50 mile canyon road test drive in Denver, DEN. Can you help me to book a flight on May 13?

ASSISTANT: Sure, can I know your destination code and return date?

USER: My source is from Phoenix, PHX. I need to catch my return flight on May 15.

ASSISTANT: I am sorry, there are no flights available.

USER: Ok, thank you for sharing the information.

ASSISTANT: Thank you.