#include <bits/stdc++.h>
using namespace std;
bool Visited[100005];
int main() {
  int N, i, j;
  scanf("%d", &N);
  long long Ans = 0;
  for (i = 2; i <= N; ++i) {
    j = N / i;
    Ans += (2LL * (j * 1LL * (j + 1))) - 4LL;
  }
  printf("%lld\n", Ans);
  return 0;
}
