#include <fstream>

using namespace std;

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

const int N = 1000000;
int v[N + 1];

int main()
{
    int n;
    long long rez = 1;
    fin >> n;
    for (int i = 1; i <= n; i++)
      v[i] = i;
    for (int i = 2; i <= n; i++)
      if (v[i] == i)
        for (int j = i; j <= n; j += i)
          v[j] = v[j] / i * (i - 1);
    for (int i = 2; i <= n; i++)
      rez += v[i] * 2;
    fout << rez;
    return 0;
}