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.Numerics;
using System.Collections.Generic;
using System.IO;
using System.Text;

public class Solver
{
    public void Solve()
    {
        long n = rl;
        if (n == 1)
        {
            Console.WriteLine(0);
        }
        else
        {
            long p = 0, q = 0;
            long s = (long)Math.Sqrt(n);
            for (long i = 1; i <= s; i++)
            {
                if (n % i == 0)
                {
                    q = n / i - 1;
                    if (n % q == i) p += q;
                }
            }
            Console.WriteLine(p);
        }
    }

    int ri { get { return sc.Integer(); } }
    long rl { get { return sc.Long(); } }
    double rd { get { return sc.Double(); } }
    string rs { get { return sc.Scan(); } }
    public StreamScanner sc = new StreamScanner(Console.OpenStandardInput());

    private const int mod = 1000000007;
    int digit10(int n) { int p = 1; while (p <= n) { p *= 10; } return p % mod; }
    int abs(int n) { return (n > 0) ? n : -n; }
    int gcd(params int[] n) { int p = n[0]; for (int i = 1; i < n.Length; i++) { p = gcd(p, n[i]); } return p; }
    int gcd(int a, int b) { return (a == 0) ? b : gcd(b % a, a); }
    int lcm(params int[] n) { int p = n[0]; for (int i = 1; i < n.Length; i++) { p = lcm(p, n[i]); } return p; }
    int lcm(int a, int b) { return a * b / gcd(a, b); }
    int max(params int[] n) { int p = n[0]; for (int i = 1; i < n.Length; i++) { p = (p > n[i]) ? p : n[i]; } return p; }
    int min(params int[] n) { int p = n[0]; for (int i = 1; i < n.Length; i++) { p = (p < n[i]) ? p : n[i]; } return p; }
    void YN(bool t) { Console.WriteLine(t ? "YES" : "NO"); }
    void Yn(bool t) { Console.WriteLine(t ? "Yes" : "No"); }
    void yn(bool t) { Console.WriteLine(t ? "yes" : "no"); }
    string clip(string s, int start, int count)
    {
        if (start + count < s.Length) { s = s.Remove(start + count); }
        if (start > 0) { s = s.Remove(0, start); }
        return s;
    }
}

static class Program
{
    static public void Main(string[] args)
    {
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Solver();
        solver.Solve();
        Console.Out.Flush();
    }

    static BigInteger power(BigInteger b, BigInteger p)
    {
        BigInteger t = b;
        BigInteger q = 1;
        while (p > 0)
        {
            if (p % 2 == 1) q *= t;
            t *= t;
            p -= p % 2;
            p /= 2;
        }
        return q;
    }
}

public class StreamScanner
{
    public StreamScanner(Stream stream) { str = stream; }
    private readonly Stream str;
    private readonly byte[] buf = new byte[1024];
    private int len, ptr;
    public bool isEof = false;
    public bool IsEndOfStream { get { return isEof; } }
    private byte read()
    {
        if (isEof) throw new EndOfStreamException();
        if (ptr >= len)
        {
            ptr = 0;
            if ((len = str.Read(buf, 0, 1024)) <= 0)
            {
                isEof = true;
                return 0;
            }
        }
        return buf[ptr++];
    }
    public char Char()
    {
        byte b = 0;
        do b = read();
        while (b < 33 || 126 < b);
        return (char)b;
    }
    public string Scan()
    {
        var sb = new StringBuilder();
        for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
            sb.Append(b);
        return sb.ToString();
    }
    public long Long()
    {
        long ret = 0; byte b = 0; var ng = false;
        do b = read();
        while (b != '-' && (b < '0' || '9' < b));
        if (b == '-') { ng = true; b = read(); }
        for (; true; b = read())
        {
            if (b < '0' || '9' < b)
                return ng ? -ret : ret;
            else ret = ret * 10 + b - '0';
        }
    }
    public int Integer() { return (int)Long(); }
    public double Double() { return double.Parse(Scan()); }
}