Problem:
Score : 700 points

Problem Statement

We have N gemstones labeled 1 through N.

You can perform the following operation any number of times (possibly zero).

Select a positive integer x, and smash all the gems labeled with multiples of x.

Then, for each i, if the gem labeled i remains without getting smashed, you will receive a_i yen (the currency of Japan).
However, a_i may be negative, in which case you will be charged money.

By optimally performing the operation, how much yen can you earn?

Constraints

All input values are integers.

1 \leq N \leq 100

|a_i| \leq 10^9

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the maximum amount of money that can be earned.

Sample Input 1

6
1 2 -6 4 5 3

Sample Output 1

12

It is optimal to smash Gem 3 and 6.

Sample Input 2

6
100 -100 -100 -100 100 -100

Sample Output 2

200

Sample Input 3

5
-1 -2 -3 -4 -5

Sample Output 3

0

It is optimal to smash all the gems.

Sample Input 4

2
-1000 100000

Sample Output 4

99000

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;

class Program{
    static void Main(){
        var n = int.Parse(Console.ReadLine());
        var a_str = Console.ReadLine().Split(' ');
        
        var a = new int[n];
        for(var i = 0; i < n; i++)
            a[i] = int.Parse(a_str[i]);
        
        var b = new bool[n];
        for(var i = 0; i < n; i++)
            b[i] = true;
        
        for(var i = n - 1; i >= 0; i--){
            long sum_value = 0;
            for(var j = i; j < n; j = (j + 1)*2 - 1){
                if(b[j])
                    sum_value += a[j];
            }
            if(sum_value < 0){
                for(var j = i; j < n; j = (j + 1)*2 - 1)
                    b[j] = false;
            }
        }
        
        long result = 0;
        for(var i = 0; i < n; i++){
            if(b[i])
                result += a[i];
        }
        
        Console.WriteLine(result);
    }
}