I've modified my .htaccess file to have the following statement

RewriteCond $1 !^index.php$
RewriteRule ^/?([^/]+)$ index.php?c=home&m=details&seo=$1 [L,NS]

This allows me to use product URL's like this: http://domain.com/product_name

However, when trying to access a file at the same level as index.php, it always calls the RewriteRule above and errors out.

I need to be able to access files like below, but each URL currently attempts to load index.php. http://domain.com/about.htm
http://domain.com/terms.htm
http://domain.com/robots.txt
etc

Any suggestions on how I can modify my htaccess file to get this to work correctly?