You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Dennis Allen here.

ASSISTANT: Dennis Allen, how may I help you today?

USER: I would like to prefer a direct flight for my holiday trip to Philadelphia. So can you book the flight ticket for me?

ASSISTANT: Sure, may I know your airport codes?

USER: The airport codes are from DCA to PHL.

ASSISTANT: Can you please share your trip dates?

USER: My trip dates are from June 06 to June 08.

ASSISTANT: Do you have connection limit preference?

USER: I need a direct flight.

ASSISTANT: Do you have any class preference?

USER: I am looking for a economy class.

ASSISTANT: Do you have any other specifications?

USER: No, that is it.

ASSISTANT: Dennis Allen, I am afraid that there is no direct flight available as per your request.

USER: Not a problem. Thank you.

ASSISTANT: Thank you for reaching us.