You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I assist you today?

USER: Please help me to book a flight ticket from IAD to LAS.

ASSISTANT: May I know your travelling dates?

USER: My travel dates are from Aug, 19 to Aug, 21.

ASSISTANT: On which name shall I reserve flight ticket?

USER: Richard Evans.

ASSISTANT: Sorry, there are no flight tickets available on your journey dates.

USER: Thank you for your information.

ASSISTANT: Thank you for reaching our service.