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