You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you?

USER: Can you aid me to book a flight ticket from IAD to LAS?

ASSISTANT: Sure, can you share your trip dates?

USER: My travel dates are Dec 4 and Dec 6 respectively.

ASSISTANT: Do you have any preferences?

USER: I prefer for single connecting flight.

ASSISTANT: May I know your name?

USER: Gary Walker here.

ASSISTANT: Sorry, there is no flight on your given dates.

USER: Thank you for the help.

ASSISTANT: Thank you for reaching us.