#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, ans = 0, a, b;
  cin >> n;
  for (long long i = 2; i <= n / 2; i++) {
    a = n / i;
    b = (a * (a + 1) / 2) - 1;
    ans += b;
  }
  cout << ans * 4;
}
