#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 22;
long long n, res;
int main() {
  ios::sync_with_stdio(false), cin.tie(0);
  cin >> n;
  for (long long i = 2; i <= n; i++)
    if (n / i > 0) res += i * (n / i - 1) * 4;
  cout << res;
  return 0;
}
