UVA - 11426 GCD - Extreme (II)

const int N = 4e6 + 5;

int t;
int cnt, p[N], phi[N];
bool book[N];
void x_x_oula()
{
	phi[1] = 1;
	f(i, 2, N)
	{
		if (!book[i]) { p[cnt++] = i;phi[i] = i - 1; }
		for (int j = 0;p[j] <= N / i;++j)
		{
			book[i*p[j]] = true;
			if (i%p[j] == 0)
			{
				phi[i*p[j]] = phi[i] * p[j];
				break;
			}
			phi[i*p[j]] = phi[i] * (p[j] - 1);
		}
	}
}
int ans[N];
int main()
{		

	//cin >> t;
	x_x_oula();
	int n;
	f(d, 1, N)
	{
		for (int i = 2 * d;i <= N;i += d)
			ans[i] += d * phi[i / d];
	}
	while (cin >> n && n)
	{
		
		ll re = 0;
		f(i, 2, n)re += ans[i];
		cout << re << endl;
	}
	return 0;
}