[ Telerik C#] LOOPS - EX 5

//Write a program that calculates N!*K! / (K-N)! for given N and K (1<N<K).
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ex4
{
    class Program
    {
        static void Main(string[] args)
        {
            int numberN, numberK;
            string input;
            int sum = 0;

            do
            {
                Console.Write("Въведете число N: ");
                input = Console.ReadLine();
            }
            while (!(int.TryParse(input, out numberN) && (numberN > 0)));

            do
            {
                Console.Write("Въведете число K: ");
                input = Console.ReadLine();
            }
            while (!(int.TryParse(input, out numberK) && (numberK < numberN)));

            int factorialN = 1;

            for (int counter = 1; counter <= numberN; counter++)
            {
                factorialN *= counter;

            }

            Console.WriteLine("The factorial of {0} is {1}", numberN, factorialN);

            int factorialK = 1;

            for (int counter = 1; counter <= numberK; counter++)
            {
                factorialK *= counter;

            }

            Console.WriteLine("The factorial of {0} is {1}", numberK, factorialK);

            int difference = numberN - numberK;
            int factorialDifference = 1;

            for (int counter = 1; counter <= difference; counter++)
            {
                factorialDifference *= counter;

            }
            Console.WriteLine("The factorial of {0} is {1}", difference, factorialDifference);

            Console.WriteLine("N!*K! / (K-N)! = {0}", (factorialN * factorialK) /factorialDifference );
        }
    }
}