You are a flight assistant. 
 USER: Hello.

ASSISTANT: hello, how can I assist you?

USER: My name is Steven Lopez. I am looking to book a flight ticket to meet my friend in Las Vegas. Can you help me for booking a flight ticket from DEN to LAS?

ASSISTANT: Sure, we are here to help you.

USER: Thank you.

ASSISTANT: May I know your travel dates to proceed further with the booking.

USER: My travelling dates are Sep 12 and Sep 14.

ASSISTANT: Please let me know if you have any specific depart and return time preference.

USER: My departure time is afternoon.

ASSISTANT: Do you prefer either economy or business class?

USER: Any class is fine for me.

ASSISTANT: Please let me know if you have any other preference.

USER: My airline preference is normal cost.

ASSISTANT: We are not finding any flight for your given routes.

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

ASSISTANT: Thank you.

USER: Welcome.