D. Fun with Integers

time limit per test

 seconds

memory limit per test

 megabytes

input

standard input

output

standard output

You are given a positive integer n

greater or equal to . For every pair of integers a and b (≤|a|,|b|≤n), you can transform a into b if and only if there exists an integer x such that <|x| and (a⋅x=b or b⋅x=a), where |x| denotes the absolute value of x

.

After such a transformation, your score increases by |x|

points and you are not allowed to transform a into b nor b into a

anymore.

Initially, you have a score of 

. You can start at any integer and transform it as many times as you like. What is the maximum score you can achieve?

Input

A single line contains a single integer n

(≤n≤

) — the given integer described above.

Output

Print an only integer — the maximum score that can be achieved with the transformations. If it is not possible to perform even a single transformation for all possible starting integers, print 

.

Examples

Input

Copy

Output

Copy

Input

Copy

Output

Copy

Input

Copy

Output

Copy

Note

In the first example, the transformations are →→(−)→(−)→

.

In the third example, it is impossible to perform even a single transformation.

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

int main()

{

    ll n;

    cin >> n;

    ll ans = ;

    for (ll i = ; i <= n/; i++) {

        ll cnt = n/i;

        ans += *(+cnt)*(cnt-)/;

    }

    cout << ans << endl;

    return ;

}