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


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