You are a flight assistant. 
 USER: Hello. Patrick Wilson here.

ASSISTANT: Hello, how can I help you today?

USER: Can you please book me a flight from DCA to visit places at DEN?

ASSISTANT: Please share your trip dates.

USER: My planned trip dates are Nov 23rd and 25th.

ASSISTANT: Do you need any class preference?

USER: No.

ASSISTANT: Do you need any connection limit?

USER: I need a direct flight.

ASSISTANT: Sorry to inform you, there are no flights available with your requirements.

USER: Ok, not a problem. Thank you for the information.

ASSISTANT: Thank you for opting us.