Calculate N! / (K! * (N-K)!)

using System;

class CalculateNFactCombinations
{
    static void Main()
    {
        Console.Write("n=");
        int n = int.Parse(Console.ReadLine());
        Console.Write("k=");
        int k = int.Parse(Console.ReadLine());
        double factNk = 1;

        double factTempNk = 1;
        if (n >= 1 && n > k && n < 100)
        {

            for (int i = n; i > k; i--)
            {
                factNk *= i;
            }
            double temp = n - k;
            for (int i = 1; i <= temp; i++)
            {
                factTempNk *= i;
            }
            Console.WriteLine(factNk/factTempNk);
        }
        else
        {
            Console.WriteLine("Error Bad input!");
        }
    }
}