#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;
int n;
int main() {
  scanf("%d", &n);
  long long res = 0;
  for (int i = 2; i <= n / 2; ++i) {
    long long buf = ((long long)n / i) * (((long long)n / i) + 1) - 2;
    res += buf * 2;
  }
  printf("%lld", res);
  return 0;
}
