#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
 
const int NMAX = 1e6 + 5;
int phi[NMAX], n;
long long sol;
 
int main()
{
    f >> n;
    for(int i = 1; i <= n; i++) {
        phi[i] = i;
    }
    for(int i = 2; i <= n; i++) {
        if(phi[i] == i) {
            for(int j = i; j <= n; j += i) {
                phi[j] /= i;
                phi[j] *= (i-1);
            }
        }
    }
    sol = 1;
    for(int i = 2; i <= n; i++) {
        sol += 2 * phi[i];
    }
    g << sol;
    return 0;
}