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 PYTHON):

Solution:
def num_divisors_table(n):
    table = [0] * (n + 1)
    
    for i in xrange(1, n + 1):
        for j in xrange(i, n + 1, i):
            table[j] += 1
    
    return table
  
n = int(input())  
a =  num_divisors_table(n)
ans = 0
for i in range(n+1):
  ans += i*a[i]
print(ans)