RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^@(.*?)$ users/profile.php?un=$1 [NC,L]

$name = isset($_GET['un']) ? trim($_GET['un']) : '';
$name = functions::rus_lat(mb_strtolower($name));
if (!empty($name)) {
    if (mysql_result(mysql_query("SELECT COUNT(*) FROM `users` WHERE `name` = '" . mysql_real_escape_string($name) . "' LIMIT 1;"), 0) != 0)
        $user = mysql_result(mysql_query("SELECT `id` FROM `users` WHERE `name` = '" . mysql_real_escape_string($name) . "' LIMIT 1;"), 0);
        else $user = -1;
}