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;
const int maxn=1e6+3;
typedef long long ll;
int n;
int main(){
	scanf("%d",&n);
	ll sum=0;
	for(int i=1;i<=n;i++)
	sum+=1ll*(1+n/i)*(n/i)/2*i;
	cout<<sum<<endl;
	
	
}