You are a flight assistant. 
 USER: Hello. My name is David Adams.

ASSISTANT: Hello, how may I help you?

USER: I would like to travel from IAD to LAS, could you help me out?

ASSISTANT: Sure, may I know your planned travel dates?

USER: My preferable dates are from 06/23 to 06/25.

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

USER: That's ok. Thank you, have a good day.

ASSISTANT: You are most welcome.