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;

public class Main {

	public static void main(String[] args) {
		// TODO 172_D
		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();

		// Scannerクラスのインスタンスをクローズ
		sc.close();

		long ans = 0;

		for(int i=1; i<=N; i++){
			long kakeMax = N/i;

			ans += kakeMax*(kakeMax+1)*i / 2;
		}

		System.out.println(ans);
	}
}