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 {

    static Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        int n = sc.nextInt();
        long ans = calc(n);
        System.out.println(ans);
    }

    private static long calc(int n) {
        long[] memo = new long[n + 1];
        for (int i = 1; i <= n; i++) {
            int j = 1;
            while (i * j <= n) {
                memo[i * j]++;
                j++;
            }
        }
        long sum = 0;
        for (int i = 1; i < memo.length; i++) {
            sum += i * memo[i];
        }
        return sum;
    }

}