#!/usr/bin/perl

# http://perlmonks.org/?node_id=1186417

use strict;
use warnings;
use Algorithm::Diff qw(traverse_sequences);

my @one = do { local @ARGV = $ARGV[0]; <> };
my @two = do { local @ARGV = $ARGV[1]; <> };
my $wantedoldline = $ARGV[2];

my $oldline = my $newline = 0;

traverse_sequences( \@one, \@two,
  {
  MATCH => sub
    {
    $oldline++;
    $newline++;
    if( $oldline == $wantedoldline )
      {
      print "$newline\n";
      exit;
      }
    },
  DISCARD_A => sub { $oldline++ },
  DISCARD_B => sub { $newline++ },
  } );

print "0\n";
[download]