#include <bits/stdc++.h>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
const int Nm = 1000000;

int t[Nm];
long sol = 1;

int main()
{
   int N;
   fin >> N;

   for (int i = 1; i <= N; i++)
    t[i] = i;

   for (int i = 2; i <= N; i++)
   {
    if (t[i] == i)
        for (int j = i; j <= N; j += i)
            t[j] = t[j] / i * (i-1);
        sol += 2 * t[i];
    }


   fout << sol;
   return 0;
}