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.Scanner;
class Main {
	public static void main(String[] a) {
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		long sum=0;
		for(long i = 1 ; i <= n ; i++) {
			sum+=((n/i)*i+i)*(n/i)/2;
		}
		System.out.println(sum);
	}
}