#include <bits/stdc++.h>
using namespace std;
typedef double db;
int n;
int main() {
  cin >> n;
  long long ans = 0;
  for (int i = 2; i <= n; i++) {
    long long k = 2;
    while (i * k <= n) {
      ans += k;
      k++;
    }
  }
  cout << ans * 4;
  return 0;
}
