You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I need to book a ticket from IAD to LAS. My travelling dates are from 05/21 to 05/23.

ASSISTANT: May I know your name please?

USER: I'm Helen Wright.

ASSISTANT: Sorry, no flights has been found.

USER: That's ok.

ASSISTANT: Ok, thank you for choosing us.

USER: You are welcome.