Sum And Product

using System;

namespace SumAndProduct
{
    class Program
    {
        static void Main(string[] args)
        {
            int num = int.Parse(Console.ReadLine());
            bool isFound = false;

            for (int i = 1; i < 9; i++)
            {
                for (int j = 9; j > i; j--)
                {
                    for (int k = 0; k < 9; k++)
                    {
                        for (int l = 9; l > k; l--)
                        {
                            if ((i + j + k + l) == i * j * k * l && num % 10 == 5)
                            {
                                Console.WriteLine($"{i}{j}{k}{l}");
                                isFound = true;
                            }
                            if (i * j * k * l / (i + j + k + l) == 3 && num % 3 == 0)
                            {
                                Console.WriteLine($"{l}{k}{j}{i}");
                                isFound = true;
                            }
                            if (isFound)
                            {
                                break;
                            }
                        }
                        if (isFound)
                        {
                            break;
                        }
                    }
                    if (isFound)
                    {
                        break;
                    }
                }
                if (isFound)
                {
                    break;
                }
            }
            if (!isFound)
            {
                Console.WriteLine("Nothing found");
            }
        }
    }
}

РЕШЕНИЕ С ТЕРНАРЕН ОПЕРАТОР И Environment.Exit(0):

using System;

namespace SumAndProduct
{
    class Program
    {
        static void Main(string[] args)
        {
            int num = int.Parse(Console.ReadLine());

            for (int i = 1; i < 9; i++)
            {
                for (int j = 9; j > i; j--)
                {
                    for (int k = 0; k < 9; k++)
                    {
                        for (int l = 9; l > k; l--)
                        {
                            if ((i + j + k + l) == i * j * k * l && num % 10 == 5
                                || (i * j * k * l / (i + j + k + l)) == 3 && num % 3 == 0)
                            {
                                Console.WriteLine((i + j + k + l) == i * j * k * l ? $"{i}{j}{k}{l}" : $"{l}{k}{j}{i}");
                                Environment.Exit(0);
                            }
                        }
                    }
                }
            }
            Console.WriteLine("Nothing found");
        }
    }
}