#include <fstream>
//#include <iostream>
using namespace std;
ifstream cin("fractii.in");
ofstream cout("fractii.out");
const int NMAX = 1e6;
int phi[NMAX + 3], i, j;
void ciur()
{
    for (i = 2; i <= NMAX; i++)
        phi[i] = i;
    for (i = 2; i <= NMAX; i++)
        if (phi[i] == i)
        for (j = i; j <= NMAX; j += i)
            phi[j] = phi[j] / i * (i - 1);
}
int main(){
    ciur();
    int n;
    long long ans = 1;
    cin >> n;
    for (i = 2; i <= n; i++)
        ans += 2 * phi[i];
    cout << ans;
}