// fractii_info_arena.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

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

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

long long f[1000000];

int main()
{
	long long n;
	
	fin >> n;
	if (n == 0) {
		fout << 0;
		return 0;
	}

	for (long long i = 1; i <= n; i++)
		f[i] = i;

	int suma = 1;

	for (long long i = 2; i <= n; i++) {
		if (f[i] == i) {
			f[i] --;

			for (long long j = 2; j * i <= n; j++) {
				f[j * i] = f[j * i] / i * (i - 1);
			}
		}
		suma += 2 * f[i];

	}

	fout << suma;
}