Problem:
Score : 500 points

Problem Statement

Snuke received a positive integer N from Takahashi.
A positive integer m is called a favorite number when the following condition is satisfied:

The quotient and remainder of N divided by m are equal, that is, \lfloor \frac{N}{m} \rfloor = N \bmod m holds.

Find all favorite numbers and print the sum of those.

Constraints

All values in input are integers.

1 \leq N \leq 10^{12}

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

8

Sample Output 1

10

There are two favorite numbers: 3 and 7. Print the sum of these, 10.

Sample Input 2

1000000000000

Sample Output 2

2499686339916

Watch out for overflow.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;

class Diverta_2019_D
{
    static void Main(string[] args)
    {
        long N = long.Parse(Console.ReadLine());

        long sum = 0;
        long sqrt = (int) Math.Sqrt(N);


        for (long i=1; i<sqrt+1; i++)
        {
            long a = (N-i) / i;
            if ((N-i) % i==0 && i<a) sum += a;
        }

        Console.WriteLine(sum);
    }
}