Mod Rewrite php htacess

Mod Rewrite php htacess

I'm trying to use clean urls on my website for better SEO. I'M doing so
doing using mod rewrite with htaccess. The Url is as follows
http://mywebsite.com/s.php?share=100 and I would like to accept urls like
http://mywebsite.com/s/100 or whatever number a user chooses. I'm using
this rewrite regex expression but it is not working as expected
RewriteEngine On
RewriteCond %{REQUEST_FILENAME}!-f
RewriteCond %{REQUEST_FILENAME}!-d
RewriteRule ^([a-z]+)/([a-z\-]+)$ /$1/$2.php
RewriteRule ^share/([^/]*)$ /s.php?share=$1 [L]
Can anyone point me as to what I'm doing wrong?