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)

namespace diverta2019.D
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using static System.Console;

    public class Program
    {
        public static void Main(string[] args)
        {
            var n = long.Parse(ReadLine());
            WriteLine(Solve(n));
        }

        public static IEnumerable<long> GetDividors(long n)
        {
            var max = (long)Math.Sqrt(n);
            for (int i = 1; i <= max; i++)
            {
                if (n % i == 0)
                {
                    yield return i;
                    if (i * i != n) yield return n / i;
                }
            }
        }

        public static long Solve(long n) => GetDividors(n).Where(k => k >= 2).Select(k => k - 1)
                .Where(i => n % i == n / i)
                .Sum();
    }
}