#include <fstream>

using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");

const int N_MAX = 1e6;
int indEuler[N_MAX + 1];

void Eratosthenes() {
	for(int i = 1; i < N_MAX; ++i)
		indEuler[i] = i;

	for(int d = 2; d <= N_MAX; ++d)
		if(indEuler[d] == d)
			for(int i = d; i <= N_MAX; i += d)
				indEuler[i] = indEuler[i] / d * (d - 1);
}

int main() {
	Eratosthenes();

	int n;
	fin >> n;
	long long sum = 0;
	for(int i = 1; i <= n; ++i)
		sum += indEuler[i];

	sum <<= 1;
	sum -= indEuler[1];

	fout << sum << '\n';

	fin.close();
	fout.close();
	return 0;
}