You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I would like to visit Las Vegas to meet my old friend, please help me in booking a ticket from DCA to LAS.

ASSISTANT: Sure, may I know your travel dates?

USER: My planned travel dates are on Feb 25 and Feb 27.

ASSISTANT: Do you have any preferences?

USER: I prefer normal-cost airline for this trip.

ASSISTANT: Do you have any other preferences?

USER: I need a connecting flight.

ASSISTANT: Please mention your name to book the flight ticket.

USER: My name is Alexander Lopez.

ASSISTANT: Sorry, I did not find any flights for you.

USER: Ok, no problem. Thank you for your information.

ASSISTANT: Thank you reaching us.