06.Calculate N! / K!

using System;

class Calculate2Factoriel
{
    static void Main()
    {
        //input
        Console.Write("Enter number for n factoriel ");
        Console.Write("in the range 1<k<n<100:");
        int numN = int.Parse(Console.ReadLine());
        Console.WriteLine("\n");
        if (numN<= 2 || (numN >= 100))
        {
            Console.WriteLine("Invalide range!");
            Console.WriteLine("\n");
            return;
        }
        Console.Write("Enter number for k factoriel ");
        Console.Write("in the range 1<k<n<100:");
        int numK = int.Parse(Console.ReadLine());
        Console.WriteLine("\n");
        if ((1 >=numK)||(numK>=100)||(numK>numN ))
        {
            Console.WriteLine("Invalid range.");
            Console.WriteLine("\n");
            return;
        }
        int factorielN = 1;
        int factorielK = 1;
        double devisionNK = 0;
        //logic
        for (int i = 1, j=1; i <=numN;j++,i++)
        {
            factorielN = factorielN * i;
            if (j <=numK)
            {
                factorielK = factorielK * j;
            }
        }
        devisionNK =(double) factorielN /(double) factorielK;
        //output
        Console.WriteLine("{0}", devisionNK);
        Console.WriteLine("\n");
    }
}