#include <fstream>
#define NMAX 1000000

using namespace std;

ifstream cin ("fractii.in");
ofstream cout ("fractii.out");

int f[NMAX + 1];

int main() {
  int n, i, j;
  long long sol;
  cin >> n;

  sol = 1;
  for (i = 2; i <= n; i++) {
    sol += (i - 1 - f[i]) * 2;
    if (f[i] == 0) {
      for (j = 2 * i; j <= n; j += i)
        f[j] += ((j / i) - 1);
    }
  }

  cout << sol;
  return 0;
}