#!/usr/bin/perl -w

use strict;

my($replacepos,$replacestr)=@ARGV;

my $BLOCKSIZE = 10;
my $buf;
my $pos = 0;
while (read(STDIN,$buf,$BLOCKSIZE))
{
  # Does this contain our byte?
  if ( ($replacepos >= $pos) && ($replacepos < ($pos + length($buf))))
  {
    print substr($buf,0,$replacepos-$pos), 
	  $replacestr, 
	  substr($buf,$replacepos-$pos+1);
  }
  else
  {
    print $buf;
  }
  $pos += length($buf);
}