#include <fstream>
#include <cmath>
#define sz 1000001
using namespace std;
int n, phi[sz];
long long sol;

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

int main()
{
    fin >> n;

    for (int i = 1; i <= n; i++)
        phi[i] = i;

    sol = phi[1];

    for (int i = 2; i <= n; i++)
    {
        if (phi[i] == i)
        {
            for (int j = i; j <= n; j += i)
                phi[j] -= phi[j] / i;
        }

        sol += 2 * phi[i];
    }

    fout << sol;

    return 0;
}