#!/usr/bin/perl -w
use strict;
use warnings;
use Math::Primality qw/is_prime/;
$|++;
my $limit = shift || 2_000_000;
my $sum = 5; # 2 + 3
for my $n (5..$limit) {
next unless ( $n % 2 ); # don't check even numbers
$sum += $n if is_prime($n);
}
print "sum of first $limit primes = $sum\n";