You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: Could you please help me with booking ticket from DCA to OAK?

ASSISTANT: May I know your desired travel dates please?

USER: Ok, my trip dates are from Nov 18 to 20.

ASSISTANT: Do you have any specifications?

USER: I need a direct flight.

ASSISTANT: May I know your name please?

USER: Sure, I am Janet Garcia.

ASSISTANT: Sorry to say, there is no flight on your desired travel dates.

USER: It's ok, thank you.

ASSISTANT: Thank you for opting us.