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 JAVA):

Solution:
import java.util.*;
public class Main{
   public static void main(String[] args) {
     Scanner sc = new Scanner(System.in);
     int n = sc.nextInt();
     long ans=0;
     for(int i=1;i<=n;i++){
      for(int j=1;j<=n/i;j++){
       ans += i*j;
      }
     }
     System.out.println(ans);

   }
}