sub fuzz {
    my $n = shift();
    return unless defined($n);

    my $neg = ($n < 0);
    ($n) = ($n =~ /(\d+)/);
    $n += 0;
    my ($c1, $c2) = ($n =~ /^(\d{0,2}\d{3})((?:\d{3})*)$/);

    return $neg ? -$n : $n unless defined($c1);

    my $c3 = substr($c1, -3, 2, "");
    my $c4 = substr($c1, -1, 1, "");
    my $n2 = $c1 . $c3;

    my $x1 = 100 - $c3;
    my $x2 = (10 - $c3 % 10) % 10;
    $n2 += $c1
      ? (
          ($x1 <= 30 && $c1 >= 10) ? $x1
          : $x2 ? $x2
          : $c4 ? 1 : 0
        )
      : ($c4 ? 1 : 0);
    $n2 .= 0 x (length($c2) + 1);

    return $neg ? -$n2 : $n2;
}