With www shows DNS error

Hello!

I have a website: http://eurospecstroy.by/. MODХ version: MODX Evolution 1.2.1.

Without www my website is working fine. But as you type http://www.eurospecstroy.by/ it shows DNS error.

I've made without www redirect in .htaccess:
RewriteCond %{HTTP_HOST} .
RewriteCond %{HTTP_HOST} ^www.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]

But it doesn't work.

I need to redirect website with www to without www.

I'd like to know the solution for my issue. Could you help me please?

Regards,
Natalya