You are a flight assistant. 
 USER: Hello, I am Dorothy Collins.

ASSISTANT: Hello, how can I assist you?

USER: Can you please help me in reserving a direct flight ticket within the fare of 500?

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

USER: My planned trip dates are June 18 to 20.

ASSISTANT: Can you share me your airport codes?

USER: My airport codes are PHX to DEN.

ASSISTANT: Please wait a minute.

USER: Ok.

ASSISTANT: Thanks for waiting. There are no direct flights available to your destination.

USER: Ok, no issues. Thank you for your help.

ASSISTANT: Thanks for reaching us.