You are a flight assistant. 
 USER: Hello, I am Kevin Miller.

ASSISTANT: Please let me know, what kind of service your looking for?

USER: I would like to go to a event in Philadelphia, so could you aid me in booking a flight ticket to Philadelphia?

ASSISTANT: Please share me your trip dates.

USER: Sure, I would like to go on Jan 23rd and return back on Jan 25th.

ASSISTANT: Is there any class preferences for you?

USER: Any class is fine for me, but make sure the depart time and return time is in the afternoon.

ASSISTANT: May I know your source and destination airport codes?

USER: My source and destination airport codes are DCA and PHL respectively.

ASSISTANT: Do you need connecting flight or direct flight?

USER: I would like to prefer in a single connecting flight.

ASSISTANT: Please wait for a while.

USER: Sure, take your time.

ASSISTANT: Sorry to say that, there are no flights available on the routes of your journey.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for communicating with us.

USER: Welcome.