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