#! /usr/bin/perl -wi
use strict;

my @last;

while (defined (my $line = <>))
{
    unless ($line =~ /^(fg|ls|l|s|sl|cd -|cd ..)$/
	    or grep { $line eq $_ } @last)
    {
	print $line;
	$last[1] = $last[0] if defined $last[0];
	$last[0] = $line;
    }
}