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>
#define int long long
using namespace std;
signed main()
{
	int n,ans=0;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		int x=i,y=n/i*i,z=(y-x)/i+1;
		ans+=(x+y)*z/2;
	}
	cout<<ans<<endl;
	return 0;
}