Regex in mod_rewrite to match URLs NOT ending with this OR that

What is the regex for this?

Match if string

• NOT ( ends in .php OR ends in .html OR contains / )

Thank you!

Edit: I need the NOT part because the expression is to be used on an Apache mod rewrite, since I can't change the logic of mod_rewrite to avoid the NOT.

Edit: My initial effort was ([^/]+)(\.html)$(^\.php)$ - which is monstrously wrong