#include <fstream>
#include <vector>
using namespace std;
int n, i, j;
long long solutie = 1;
ifstream f("fractii.in");
ofstream g("fractii.out");

int main() {
	vector<int> phi;
	f >> n;
	for (i = 0; i <= n; ++i) phi.push_back(i);
	for (i = 2; i <= n; ++i) {
		if (i == phi[i]) {
			--phi[i];
			for (j = 2 * i; j <= n; j += i) phi[j] = (phi[j] / i) * (i - 1);
		}
	}
	for (i = n; i > 1; --i) solutie += 2LL * phi[i];
	g << solutie;
}