You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I guide you?

USER: I am Jack White. I would like to book a flight ticket from DEN to JFK.

ASSISTANT: Sure, can I know your preferable dates?

USER: I am planning to start on 10/21 and return back on 10/23.

ASSISTANT: I am sorry, there are no flights available.

USER: Ok, no problem. Thank you for the information.

ASSISTANT: Thank you, have a good day.