#!/usr/bin/perl -w
# Shift the alpha characters based on sum of coordinate values.

use strict;
use constant RANGE => 4;

# Rotate an alpha character by the specified amount, preserving case.
sub rot($$)
{
   my ($c, $s) = @_;

   my $base = ($c =~ /[a-z]/) ? ord('a')
                              : ($c =~ /[A-Z]/) ? ord('A') : undef;
   return defined($base) ? chr((ord($c) - $base + $s) % 26 + $base) : $c;
}


while( my $line = <> )
{
   my $x = 0;
   foreach my $c (map {chr $_} unpack "C*", $line)
   {
      print rot($c, ($x + $. * 2) % RANGE);
      $x++;
   }
}