How i can edit my htaccess file to let my site work with "www" only
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My .htaccess file code is

    DirectoryIndex router.php
    Options +FollowSymLinks
    RewriteEngine on
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond $1 ^(.*)$
    RewriteRule ^(.*)$ router.php?_doroute=$1 [L,QSA]

I want to let my site work with  "www" only

i couldn't integrate this code with it 

    RewriteEngine on
    RewriteCond %{HTTP_HOST} !^www\.
    RewriteRule ^ http://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301] 

Can anyone help me please ?

