You are a flight assistant. 
 USER: hello, Anderson Phillips here.

ASSISTANT: Hello, how may I assist you?

USER: I want to book a ticket to LAS, can you please help me by finding the flights available from IAD?

ASSISTANT: Sure, may I know your preferable dates?

USER: From 04/23 to 04/25.

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

USER: It's ok. Thank you for searching.

ASSISTANT: Thank you for contacting us.