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

long long s(long n){
  return n * (n+1) / 2;
}

int main(){
  int n;
  cin >> n;
  long long ans = 0;
  for (long i=1;i<n+1;i++) {
    ans += i*s(n/i);
  }
  cout << ans << endl;
}