#include <bits/stdc++.h>
using namespace std;
const int N = 1000010;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n, phi[N];
int64_t sol = 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)
            for(int j = i; j <= n; j += i)
                phi[j] = phi[j] / i * (i - 1);
        sol += 2 * phi[i];
    }
    g << sol;

    return 0;
}