You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I serve you?

USER: Susan Robinson here. I would like to visit DCA, can you help me to book a flight on 04/25?

ASSISTANT: Sure, I can help you. When would you like to return?

USER: I would like to return on 04/27.

ASSISTANT: Where would you like to start from?

USER: My preferred source airport code is DEN.

ASSISTANT: Do you need any break?

USER: Yes, I need a connecting flight.

ASSISTANT: We found a AA airline, flight number:1016 and the price is 200.

USER: Proceed with booking.

ASSISTANT: Your flight ticket has been processed.

USER: Thank you.

ASSISTANT: Thank you.