#include <iostream>
#include <fstream>

using namespace std;
 
ifstream fin("fractii.in");
ofstream fout("fractii.out");
 
int n, f[1000005];
long long int suma = 1LL;
 
int main() {
	fin >> n;
	for(int i = 1; i <= n; i++) {
		f[i] = i;
	}
	for(int i = 2; i <= n; i++) {
		if(f[i] == i) {
			f[i]--;
			for(int j = 2; j * i <= n; j++) {
				f[j * i] = f[j * i] / i * (i - 1);
			}
		}
		suma += 2 * f[i];
	}
	fout << suma;
	return 0;
}