#include <fstream>

#define MAXN 1000005

using namespace std;

ifstream f ("fractii.in");
ofstream g ("fractii.out");

int n;
double phi[MAXN];
long long sum = 1;

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){
            phi[i] = i - 1;

            for(int p = 2 * i; p <= n; p += i){
                phi[p] *= (i - 1);
                phi[p] /= i;
            }
        }
        sum += 2 * phi[i];
    }

    g << sum << '\n';
}