$sum = 0;
for ($i = 11; $i < 1000000; $i+=2) {
  $j = $i;
  while ($j ne '' && isprime($j)) {
    $j = substr($j,1);
  }
  if ($j eq '') {
    $j = $i;
    while ($j ne '' && isprime($j)) {
      $j = substr($j,0,-1);
    }
    if ($j eq '') {
      print "$i\n";
      $sum += $i;
    }
  }
}
print "----\n$sum\n";

<STDIN>;


sub isprime {
    my $num = $_[0];
    my $val = 'prime';
    if ($num =~ /^\d+$/ && $num >= 2) {
        my $mod = 2;
        my $div = int sqrt $num;
        while ($mod <= $div) {
            ($num % $mod) == 0 ? ($val = 'composite', last) : $mod++;
        }
    } else { $val = 'neither'; }
    if ($val eq 'prime') {
      return 1;
    } else {
      return 0;
    }
}