You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: My name is Mark Thomas. I would like to visit Space Needle on my friend's birthday, can you please book the ticket from DEN to SEA?

ASSISTANT: Can I know your travel dates?

USER: The dates are from 06/04 to 06/06.

ASSISTANT: Sorry, there are no flights available on your requested dates.

USER: That's ok. Thank you for your time.

ASSISTANT: Welcome.