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;

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