#include <bits/stdc++.h>
using namespace std;
const long long int N = 1e5 + 2;
const long long int inf = 1e16 + 9;
const long long int mod = 1e9 + 7;
int main() {
  long long int n, i, j, k, x, ans = 0;
  cin >> n;
  for (i = 2; i <= n / 2 + 1; i++) {
    x = n / i;
    if (x == 0) continue;
    k = (x * (x + 1)) / 2;
    ans = ans + k - 1;
  }
  cout << 4LL * ans << endl;
  return 0;
}
