#include <bits/stdc++.h>
using namespace std;
long long fac[1000001];
int main() {
  long long n, ans = 0, c = 0, mx = 0, tmp, tmp2, lg;
  cin >> n;
  for (long long i = 2; i < n; i++) {
    tmp = n / i;
    tmp = tmp * (tmp + 1) / 2 - 1;
    ans += (tmp * 4);
  }
  cout << ans << "\n";
  return 0;
}
