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<?php
function isPrime($num)
{
if ($num == 2 || $num == 3) { return 1; }
if (!($num%2) || $num<1) { return 0; }
for ($n = 3; $n <= $num/2; $n += 2) {
if (!($num%$n)) {
return 0;
}
}
return 1;
}
for ($i = 2; $i <= N; $i++) {
if (isPrime($i)) {
$sum += $i;
}
}