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;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Linq;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Security.Cryptography;

class Program
{
    const string Yes = "Yes";
    const string No = "No";
    const char White = '.';
    const char Black = '#';
    const long Mod = 1000000007;

    static void Main(string[] args) {
#if DEBUG
        MyDebugger.Test(process, "../TextFile1.txt");
#else
        checked {
            object ret = process(new StreamReader(Console.OpenStandardInput()));
            Console.WriteLine(ret);
        }
#endif
    }

    static object process(TextReader input) {
        var n = long.Parse(input.ReadLine());

        long sum = 0;

        foreach(var i in Aliquot(n)) {
            if(i == 1) continue;
            var m = i - 1;
            if (n / m == n % m) sum += m;
        }

        return sum;
    }

    //約数列挙（1とnを含む降順）
    static List<long> Aliquot(long n) {
        if(n==1) return new List<long>{ 1 };

        var ret = new List<long>();
        for (long j = 1; j <= Math.Sqrt(n); j++) {
            if (n % j != 0) continue;
            ret.Add(n/j);
        }
        ret.Add(1);

        return ret;
    }

    static long[] ToIntArray(string strs, int n) {
        var ret = new long[n];
        var spl = strs.Split(' ');
        for (int i = 0; i < n; i++)
            ret[i] = long.Parse(spl[i]);
        return ret;
    }
}