You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I be at your service today?

USER: Could you please book a ticket to Oakland with a connecting flight?

ASSISTANT: Sure, can you please let me know your preferred journey dates?

USER: My journey dates are Jan 11 and Jan 13.

ASSISTANT: Do you have any class preference?

USER: No.

ASSISTANT: Please assign your take off airport code.

USER: I want to take off from DEN.

ASSISTANT: In which airlines you prefer to travel?

USER: I would prefer a normal-cost airline.

ASSISTANT: Is there any other preferences?

USER: I want to return in the morning.

ASSISTANT: May I know your good name please?

USER: My name is Nicholas Lee.

ASSISTANT: We found a United airlines, price is 200 in economy class, with one stopover, and your return flight time is 5:00 AM.

USER: Ok, proceed with the booking.

ASSISTANT: Your ticket has been reserved with 1014 flight number.

USER: Thank you for your service.

ASSISTANT: Thank you for choosing our services.