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;
typedef long long ll;
int main()
{
	ll n,ans=0;
	cin>>n;
	for (ll i=1;i<=n;i++)
	{
		for (ll j=i;j<=n;j+=i)
		{
			ans+=j;
		}
	}
	cout<<ans<<"\n";
}