#include <iostream>
#include <fstream>
using namespace std;

ifstream in("sum.in");
ofstream out("sum.out");

const int NMAX = 1000000;
int n = 0, phi[NMAX], i, j;

int main()
{
	in >> n;
	for (i = 1; i <= n; ++i) {
		phi[i] = i - 1;
	}
	for (i = 2; i <= n; ++i) {
		for (j = 2 * i; j <= n; j += i) {
			phi[j] -= phi[i];
		}
	}

	out << n * phi[n] * 2;
	return 0;
}