You are a flight assistant. 
 USER: Hi. Donald Walker here.

ASSISTANT: Hello. Donald, how can I help you?

USER: Please book a ticket from DEN - DCA. As I am visiting white house to celebrate Christmas.

ASSISTANT: Sure.

USER: These are the dates 11/09 and 11/11.

ASSISTANT: May I know the travelling dates of your journey? Ok, please wait for a moment.

USER: Sure.

ASSISTANT: Thank you for waiting Donald. There are no flights found on your request.

USER: It is not a problem. Thank you.

ASSISTANT: Thank you for approaching us, have a nice day. You are welcome.