$y=1;
for$h(2..<>){
	$x=0;
	$c=0;
	for$i(1..$h-1){
		$x+=1;
		$c+=1;
		for$j(1..$i-1){
			$x+=$i*$j;
			$c+=1;
		}
	}
	$y+=$x/$c;
}
print $y;