a1a
a1a
b1b
c1c
c1c
d1d
d1d
e1e
f1f
g1g
g1g
h1h
h1h
i1i
j1j

##</code><code>##

while (<DATA>) {
	chomp;
	$curr = $_;
	$line = $.;
	if ($line == 1)
	{
		$prev = $curr;
		next;
	}
	if ($line % 2 == 0 && $line > 2 && !$flag)
	{
		$prev = $curr;
		next ;
	}
	else
	{
		$flag = 0;

	}

	if ($curr eq $prev) {
	$flag = 1;
	next;	
	}
	print "$curr\n";
$prev = $curr;
}

##</code><code>##

b1b
e1e
f1f
i1i
j1j