Methods-Factorial Division

using System;
using System.Numerics;

namespace methods_exerci
{
    class Program
    {
        static void Main(string[] args)
        {
            long number = long.Parse(Console.ReadLine());
            long divide = long.Parse(Console.ReadLine());
            double result = Factorial(number) / Factorial(divide);
            Console.WriteLine($"{result:f2}");
        }

        static double Factorial(long number)
        {
            long sum2 = 1;

            if (number == 0)
            {
                sum2 = 1;
            }
            else
            {
                for (int i = 2; i <= number; i++)
                {
                    sum2 *= (i);
                }
            }
            return sum2;
        }
    }
}