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

signed main(){
	ll n; cin >> n;
	ll ans = 0;
	for(ll i = 1; i <= n; i++){
		ll p = n / i;
		ll l = p * i;
		ans += p * (i + l) / 2;
	}
	cout << ans << endl;
}