#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int N;
  scanf("%d", &N);
  long long res = 0;
  for (int i = 2; i <= N / 2; i++) {
    long long m = N / i;
    res += (m * (m + 1) / 2 - 1) * 4;
  }
  printf("%lld\n", res);
}
