use strict;

my $usage = "$0 number\n";
my $num = shift or die $usage;
my @buf = ();
my $line;
while ($line = <>) {
    chomp($line);
    if (($line =~ /^\#/) or ($line =~ /^\s*$/)) { 
	print "$line\n"; 
	next; 
    }
    push(@buf, $line);
    my $bufsz = scalar(@buf);
    if ($num == $bufsz) {
	my $i = rand($bufsz);
	print "$buf[$i]\n";
	@buf = ();
    }
}

my $bufsz = scalar(@buf);
if ($num == $bufsz) {
    my $i = rand($bufsz);
    print $buf[$i];
    @buf = ();
}