Hello.
user
Hello. How can I  help you?
assistant
I am Mark Lee. Can you please book me a ticket from DCA to SFO?
user
Your travelling dates please?
assistant
My planned trip dates are May 26th and 28th.
user
I am sorry no flights found on your route.
assistant
Ok, that's fine.
user
Thank you for choosing us.
assistant
Anyways, thanks for the information.
user