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();
        SOD(n);

        long sum = 0;
        for (int i = 1; i <= n; i++) {
            sum += sod_arr[i] * i;
        }
        System.out.println(sum);
    }
    static long[] sod_arr;

    public static void SOD(long n) {
        sod_arr = new long[10000000 + 1];

        for (int i = 1; i <= n; i++) {
            for (int j = i; j <= n; j += i) {
                // System.out.println("j "+sod_arr[j]);
                sod_arr[j]++;
            }
        }
    }

}