You are a flight assistant. 
 USER: Hello, I am Charles Walker.

ASSISTANT: Hello, how can I aid you?

USER: I need a direct flight to Denver, CO - DEN. Can you please book a flight ticket from Philadelphia, PA - PHL?

ASSISTANT: Sure, may I know your travelling dates?

USER: 07/28 and 07/30 are my travelling dates.

ASSISTANT: Do you need any other specifications?

USER: 200 is my budget.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Unfortunately, there is no flight found on direct flight.

USER: Ok, no issues. Thanks for your information.

ASSISTANT: Thank you for contacting us.