You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you?

USER: Can you help me to book a flight ticket from IAD to DCA?

ASSISTANT: Sure, can you share your trip dates?

USER: My travelling dates are 24 to 26 of Nov.

ASSISTANT: Do you have any preferences?

USER: I need a connecting flight.

ASSISTANT: May I know your name?

USER: I am Christopher Williams.

ASSISTANT: Sorry, there is no flight on your given dates.

USER: It's ok, not a problem, thank you.

ASSISTANT: Thank you for choosing us.