#!/vol/gnu/bin/perl5.6 -w
#!/usr/local/bin/perl -w
#!/usr/bin/perl -w

use strict;

unless ($ARGV[0]) {
    die "Sorry, I need at least one argumenst: sparse.pl line [offset=0] < infile > outfile."
}

my $l = $ARGV[0]; # print every l line
my $o = 0; # offset default
if ($ARGV[1]) { $o = $ARGV[1]; }

for (my $i=0; $i<$o; $i++) { <STDIN>; }

my $n = 0;
 LINE: while (<STDIN>) {
     $n++;
     if (($n-1) % $l == 0) { print $_; }
 };