$0 = 1
$1 = 1
while( $0 <= W)
  if(A[$1,$0]!=B[$1,$0])
	return ($1,$0)
  end
  $0=$0+1
  if($0==W+1)
	$0=0;
	$1=$1+1 
  end
  if($1==H+1)
    $0=W+5
  end
end