F = Map()
FF = Map()

adjust F(k, d) = {
	my (v);
	if (!mapisdefined(F, k, &v),
		v = 0;
	);
	mapput(F, k, v+d);
	return (v+d);
}
adjust FF(k, d) = {
	my (v);
	if (!mapisdefined(FF, k, &v),
		v = 0;
	);
	mapput(FF, k, v+d);
	return (v+d);
}

{
	v = -1;

	for (n = 1, 10 000,
		print (n " " v);

		old f = adjust F(v, 0);
		adjust FF(old f, -1);

		f = adjust F(v, +1);
		nb = adjust FF(f, +1);

		same = nb * f;
		diff = n - same;

		v = diff - same;
	);
}

quit