#include <fstream>
using namespace std;

const int VMAX = 1e6;

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

int ciur[VMAX + 1];

int main()
{
    int n;
    fin >> n;
    for(int d = 1; d <= n; d++)
    {
        ciur[d] = d;
    }
    for(int d = 2; d <= n; d++)
    {
        if(ciur[d] == d)
        {
            for(int m = d; m <= n; m += d)
            {
                ciur[m] = ciur[m] / d * (d - 1);
            }
        }
    }
    long long s = 1;
    for(int i = 2; i <= n; i++)
    {
        s += 2 * ciur[i];
    }
    fout << s;
    return 0;
}