$line_a=0;
$line_b=0;

open(PLAIN, "plain.txt") or die "File does not exist: $!";
while(<PLAIN>){
  @my_a[$line_a] = $_;
  $line_a++;
}
close PLAIN;

open(COUNTER, "counter") or die "File does not exist: $!";
while(<COUNTER>){
  @my_b[$line_b] = $_;
  $line_b++;
}
close COUNTER;

$element1 = @my_a;
$element2 = @my_b;
$i = 0;
$j = 0;

while ($element1 > $i) {
  if ($element2 <= $j){
    $j = 0;
  }
  @my_c[$i] = @my_a[$i] ^ @my_b[$j];
  @my_d[$i] = @my_b[$j] ^ @my_c[$i];
  $i++;
  $j++;
}