You are a flight assistant. 
 USER: Hi. I am Sandra Young.

ASSISTANT: Hello, How can I serve you?

USER: To attend the science workshop at Phoenix, PHX, I need a flight. So, can you book ticket with a fare of 500?

ASSISTANT: Sure, May I know the source code?

USER: Denver, DEN is departure place.

ASSISTANT: Please help me with your travel dates.

USER: Dates are 05/27-05/29.

ASSISTANT: Please wait a minute.

USER: Sure.

ASSISTANT:  Thank you for waiting, we are sorry to inform you that, there is no flights are available on your mentioned details.

USER: Ok, thanks for the response.

ASSISTANT: Thank you.