my $num = shift;
my $firstlen = int(length($num)/2 + .5);
my $backlen = length($num) - $firstlen;
my $first = substr($num, 0, $firstlen);
my $closest = 0;
for (1..2) {
  my $new = $first . substr(reverse($first), -$backlen);
  $closest = $new if abs($new - $num) < abs($closest - $num);
  $first += $num <=> $closest;
}

print "Closest palindrome to $num is $closest\n";