#include <bits/stdc++.h>
using namespace std;
std::map<long long, long long> factors;
void primeFactors(long long n) {
  while (n % 2 == 0) {
    factors[2]++;
    n = n / 2;
  }
  for (long long i = 3; i <= sqrt(n); i = i + 2) {
    while (n % i == 0) {
      factors[i]++;
      n = n / i;
    }
  }
  if (n > 2) factors[n]++;
}
long long i, j;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  long long ans = 0;
  for (i = 2; i <= n; i++) {
    long long x = n / (i);
    ans += (i) * (x - 1);
  }
  cout << ans * 4 << '\n';
  return 0;
}
