Divide N Factorial By K Factorial

using System;
using System.Diagnostics;
using System.Numerics;

class DivideNFactorialByKFactorial
{
    static void Main()
    {
        BigInteger numberN, numberK;
        string invalidInput = "Please enter a valid number! (1 < K < N)" + Environment.NewLine;

        while (true)
        {
            Stopwatch stopWatch = new Stopwatch();

            Console.WriteLine("Enter a value for N: ");
            while (!(BigInteger.TryParse(Console.ReadLine(), out numberN) && numberN > 1))
            {
                Console.WriteLine(invalidInput);
                Console.WriteLine("Enter a value for N: ");
            }

            Console.WriteLine("Enter a value for K: ");
            while (!(BigInteger.TryParse(Console.ReadLine(), out numberK) && numberK > 1 && numberK < numberN))
            {
                Console.WriteLine(invalidInput);
                Console.WriteLine("Enter a value for K: ");
            }

            BigInteger factorialDivision = 1;

            for (BigInteger i = numberK + 1; i <= numberN; i++)
            {
                stopWatch.Start();
                factorialDivision = factorialDivision * i;
            }

            Console.WriteLine("{0}! / {1}! = {2}" + Environment.NewLine, numberN, numberK, factorialDivision);
            stopWatch.Stop();
            TimeSpan ts = stopWatch.Elapsed;
            string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}", ts.Hours, ts.Minutes, ts.Seconds, ts.Milliseconds / 10);
            Console.WriteLine("runtime: " + elapsedTime + Environment.NewLine);
        }
    }
}