$/=-<>;
$a=1;
for(glob<>){
	$h{$_}+=$a,$_*=2 while$_<=1e9;
	$a=-$a;
}
for(sort{$a-$b}keys%h){
	$b+=$h{$_};
	$z=$b if $z<$b;
}
print$z+0;