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

int main() {
  int n;
  cin >> n;
  int64_t ans = 0;
  for (int64_t i = 1; i <= n; i++) {
    int64_t j = n/i;
    ans += i*j*(j+1)/2;
  }
  
  cout << ans << endl;
  return 0;
}