You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I assist you?

USER: Could you please book a ticket from Washington DC-IAD to Las Vegas, NV-LAS.

ASSISTANT: Sure, I am here to help you out. May I know your travelling dates please?

USER: My travelling dates are from 04/04 to 04/06.

ASSISTANT: May I know your name please?

USER: My name is Jack Walker.

ASSISTANT: Jack Walker, there are no flights available in your route.

USER: Thank you.

ASSISTANT: Thank you for reaching us.