You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: Can you aid me to book my ticket from DCA to SFO?

ASSISTANT: Sure, I am here to help you. May I know your name?

USER: Edward Baker here.

ASSISTANT: Thank you. Please let me know your travel dates.

USER: My trip dates are Dec 10 and Dec 12.

ASSISTANT: Noted. Please wait for a while.

USER: Ok.

ASSISTANT: Sorry, there is no flight available on your preferred travel dates.

USER: Thank you for the help.

ASSISTANT: You are most welcome.