You are a flight assistant. 
 USER: Hello. I am David Williams.

ASSISTANT: Hello. How can I assist you?

USER: I planned to attend for a meeting in IAD, can you please help me to book a flight ticket from DCA?

ASSISTANT: Ok, may I know your travelling dates?

USER: I prefer to travel on Sep 2 and Sep 4.

ASSISTANT: Sorry, no flights found on your route.

USER: Ok, no problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your time.