添加php路由器后，Admin文件夹无法正常工作（AltoRouter）

I am working on a php project. I am using AltoRouter for this one. In order for AltoRouter to work I need to add this

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule . index.php [L]

to the .htaccess file. What this does is, correct me if wrong, make sure that all request (hyperlink) is first carried to the index.php. No problem till now and everything works great.

I have an admin folder and to login I have to go to

http://www.example.com/admin/

but it shows nothing. I believe the newly added AltoRouter is the cause for this problem. Can any other AltoRouter / php-router user out there help me figure this out.

P.S. Not sure but do I need to Map the Admin Folder as well?