#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  long long s = 0;
  cin >> n;
  for (int i = 2; i <= n / 2; i++) {
    for (int j = 2; j * i <= n; j++) s += 4 * j;
  }
  cout << s << endl;
  return 0;
}
