#include <iostream>
#include <fstream>
#define dMAX 1000005

using namespace std;

int n, phi[dMAX];
unsigned long long int S;

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

void GeneratePhi() {
    int i, j;
    for (i = 1; i <= dMAX; i++) phi[i] = i;
    for (i = 2; i <= dMAX; i++) {
        if (phi[i] == i) {
            for (j = i; j <= dMAX; j += i) {
                phi[j] /= i;
                phi[j] = phi[j] * (i - 1);
            }
        }
    }
    for (i = 2; i <= dMAX; i++) {
        phi[i] *= 2;
    }
}

int main()
{
    fin >> n;
    GeneratePhi();
    for (int i = 1; i <= n; i++) {
        S += phi[i];
    }
    fout << S;
    return 0;
}