H6_Loops_T4_NKFactorial

//Write a program that calculates N!/K! for given N and K (1<K<N).
using System;
using System.Numerics;


class NKfactorial
{
    static void Main()
    {
        Console.WriteLine("Please enter number k, which has to be integer bigger than 1:");
        int k = int.Parse(Console.ReadLine());
        Console.WriteLine("Please enter number n, which has to be integer bigger than k:");
        int n = int.Parse(Console.ReadLine());

        BigInteger productNKFactorial = 1;
        if (k > 1 && n > k)//Checks whether input is correct.
        {
            for (int i = n; i > k; i--)
                //I do not calculate separately N! and K!, because K!
                //is contained in N! and therefore the common parts are not needed to be calculated.
            {
                productNKFactorial = productNKFactorial * i;
            }
            Console.WriteLine("The result is: {0}", productNKFactorial);
        }

        else
        {
            Console.WriteLine("Wrong input!");
        }
    }
}