#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
  int N;
  cin >> N;
  ll ans = 0;
  for (int i=1; i<=N; i++) {
    for (int j=i; j<=N; j+=i) {
      ans += j;
    }
  }
  cout << ans << endl;
}