use warnings;
use strict;

my $exclre = qr/^(?:ls?|man|cat)\b/;

my @buf;
while (<>) {
	if (/^#\d+$/ || eof()) {
		push @buf, $_ if eof();
		if (@buf>2 || @buf==2 && $buf[1]!~$exclre) {
			print @buf;
		}
		@buf=();
	}
	push @buf, $_;
}