Problem:
Score : 400 points

Problem Statement

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).

Sample Input 1

4

Sample Output 1

23

We have f(1)=1, f(2)=2, f(3)=2, and f(4)=3, so the answer is 1\times 1 + 2\times 2 + 3\times 2 + 4\times 3 =23.

Sample Input 2

100

Sample Output 2

26879

Sample Input 3

10000000

Sample Output 3

838627288460105

Watch out for overflows.

Solution in Python (3.8.2) (judge verdict: Time Limit Exceeded)

import math

N = int(input())

def count_divisor(n):

    ans = 0
    
    i=1
    while i*i <= n:
        syou, amari = divmod(n,i)
        #print(syou, amari)
        if(amari == 0):
            ans += 1
            if( syou != i):
                ans += 1
        i+=1
    return ans

ans = 0
for i in range(1, N+1):
    ans += i*count_divisor(i)

print(ans)