#include <bits/stdc++.h>
using namespace std;

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

int n;
long long nr = 1;
int Euler[1000005];

void Ciur()
{
    for (int i = 1; i <= n; ++i)
        Euler[i] = i;

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

int main()
{
    fin >> n;

    Ciur();

    for (int i = n; i > 1; --i)
    {
        int tmp = Euler[i];
        nr += 2 * tmp;
    }

    fout << nr;
    fin.close();
    fout.close();
    return 0;
}