mod_rewrite clashing

Hello

I currently have a mod_rewrite for a profile system where users can go onto other users profiles e.g

example.com/john
exampe.com/sarah

However this would cause problems if a user attempted to go on a profile that had an actual directory on my server e.g

example.com/images
example.com/files

My question is how can I add an exemption to these directories so they do not work with the mod_rewrite.

#insert before your RewriteRule
RewriteCond %{REQUEST_URI} !(images|files)

Regards,

DK