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:
# -*- coding: utf-8 -*-
import math
N=input()
A=[ 2 for _ in range(N+1)]
A[0]=0
A[1]=1

for cur in range(2,N+1):
    for i in range(cur*2,N+1,cur):
        A[i]+=1

ans=0
for i in range(1,N+1):
    ans+=i*A[i]
print ans