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