CalculateN!andK!

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

class Program
{
static void Main()
{
    Console.WriteLine("Please Enter N and K [1<N<K]");
    Console.Write("Enter N = ");
    int n = int.Parse(Console.ReadLine());
    Console.Write("Enter K = ");
    int k = int.Parse(Console.ReadLine());
    BigInteger firstFact = 1;
    BigInteger secondFact = 1;
    BigInteger thirdFact = 1;
    Console.Write("The result is: ");
    if (n < k & 1 <= n)
    {

        for (int i = 1; i <= n; i++)
        {
            firstFact *= i;
        }
        for (int q = 1; q <= k; q++)
        {
            secondFact *= q;
        }
        for (int y = 1; y <= (k - n); y++)
        {
            thirdFact *= y;
        }
        Console.Write("{0}\n ", (firstFact * secondFact) / thirdFact);
    }
    else
        Console.WriteLine("Wrong input!");
}
}