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 <iostream>
using namespace std;
int n;
int main()
{
	long long i,j,k,ans=0;
    cin>>n;
    for(i=1;i<=n;i++){
        for(j=i;j<=n;j+=i){
            ans+=j;
        }
    }
    cout<<ans;
	return 0;
}