You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Rebecca Jones here. I want to participate in Boston marathon, so please book a ticket from LAS to BOS.

ASSISTANT: Sure, may I know your travelling dates?

USER: My itinerary dates are 12/21 and 12/23.

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

USER: It's ok, thank you.

ASSISTANT: Thank you for reaching us.