You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: I am having an invitation from White House in Washington, please book me a ticket from SFO to DCA.

ASSISTANT: Sure, could you please provide your preferable travel dates?

USER: My preferable journey dates are from 07/13 to 07/15.

ASSISTANT: May I know your name to proceed further?

USER: My name is Katherine Lewis.

ASSISTANT: Katherine, I am sorry to inform you that there is no flight available at your request.

USER: Ok, no issues. Thank you for your information.

ASSISTANT: You are welcome. Thank you for contacting us.