+using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace kek
{

    class Program
    {
        static int Fact_1(int n)
        {
            Console.WriteLine("Вызов " + n);
            int f = 1;
            if (n > 1) f = n * Fact_1(n - 1);
            Console.WriteLine("Подсчет при n = " + n + " Факт = " + f);
            return f;
        }

        static int Fact_2(int n)
        {
            int f = 1;
            if (n > 1) f = Fact_2(n - 1) * n;
            return f;
        }

        static void Fact_out(int n, out int f)
        {
            if (n > 1)
            {
                n--;
                Fact_out(n, out f);
                f *= (n + 1);
            }
            else f = 1;
        }

        static void Fact_ref(int n, ref int f)
        {
            if (n > 1)
            {
                f *= n;
                n--;
                Fact_ref(n, ref f);
            }
        }

        static void Main(string[] args)
        {
            Console.WriteLine("Введите число для подсчета его факториала");
            int n = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine();
            Console.WriteLine("{0}! = {1}\n", n, Fact_1(n));
            Console.WriteLine("{0}! = {1}\n", n, Fact_2(n));
            int f;
            Fact_out(n, out f);
            Console.WriteLine("{0}! = {1}\n", n, f);
            f = 1;
            Fact_ref(n, ref f);
            Console.WriteLine("{0}! = {1}\n", n, f);
            Console.ReadKey();
        }
    }
}