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

ifstream fin("fractii.in");
ofstream fout("fractii.out");
int n, euler[1000001];

int main()
{
	fin >> n;
	unsigned long long sum = 1; // raportul 1/1

	for (int i = 2; i <= n; i++)
		euler[i] = i;

	for (int i = 2; i <= n; i++)
		if (euler[i] == i)
			for (int j = i; j <= n; j += i)
				euler[j] = euler[j] / i * (i - 1);

	for (int i = 2; i <= n; i++)
		sum += 2 * euler[i];

	fout << sum;
}