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;
typedef long long ll;
ll n,a,b,ans;
int main(void){
    cin>>n;
    for(int i=1LL;i<=n;i++){
        a=n/i;
        b=a*(a+1)/2;
        ans+=b*i;
    }
    cout<<ans<<endl;
}