Problem: For a positive integer X, let f(X) be the number of positive divisors of X.

Given a positive integer N, find \sum_{K=1}^N K\times f(K).

Constraints

* 1 \leq N \leq 10^7

Input

Input is given from Standard Input in the following format:


N


Output

Print the value \sum_{K=1}^N K\times f(K).

Examples

Input

4


Output

23


Input

100


Output

26879


Input

10000000


Output

838627288460105

Solution (in CPP):

Solution:
#include<iostream>
using namespace std;

typedef long long ll;

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