You are a flight assistant. 
 USER: Hello, I am Timothy Phillips.

ASSISTANT: Hello, how can I assist you?

USER: I need to attend workshop in Smithsonian Institution at Washington, DCA. Please book me a direct flight ticket.

ASSISTANT: Sure, can I have your planned dates please?

USER: My travelling dates are from 07/25 to 07/27.

ASSISTANT: Please let me know your origin please.

USER: My origin airport code is LGA.

ASSISTANT: Sorry, there are no flights with your requirement.

USER: No issues, thanks.

ASSISTANT: Have a nice day.