#!/usr/bin/perl -w

use strict;

if( $#ARGV < 0 )
{
   die "$0 <key>\n";
}
my $key = shift;
$key =~ s/[^a-zA-Z]//g;
$key ||= "a";
my @offsets = map {$_ <= ord('Z') ? (ord('A') - $_ + 26) % 26
                                  : $_ - ord('a')}
                  unpack 'C*', $key;

my %translate = ();
for(my $input = 0; $input < 26; $input++)
{
   for(my $offset = 0; $offset < 26; $offset++)
   {
      $translate{chr(ord('a') + $input)}{$offset} =
         chr(ord('a') + ($input + $offset) % 26);
      $translate{chr(ord('A') + $input)}{$offset} =
         chr(ord('A') + ($input + $offset) % 26);
   }
}

my $index = 0;
while( my $line = <> )
{
   foreach my $i (unpack 'C*', $line)
   {
      my $c = chr($i);
      if( $c =~ /[a-zA-Z]/ )
      {
         my $offset = $offsets[$index++];
         $index %= length($key);

         $c = $translate{$c}{$offset};
      }
      print $c;
   }
}