6.20Loops_CalculateNFibonacciNumber

using System;
using System.Numerics;

class FibonacciNumbers
{
    static void Main ()
    {
        Console.Write("Please, enter a whole positive number for N = ");
        string numberStr = Console.ReadLine();
        int numN = int.Parse(numberStr);
        if (numN < 1 || numN > 100000)
        {
            Console.WriteLine("Error - The number {0} is out of range !!!");
        }
        else
        {
            checked
            {
                BigInteger fibonacciFirst = 1;
                BigInteger fibonacciSecond = 1;
                Console.WriteLine("The First N members of Fibonacci Numbers are:");
                if (numN == 1)
                {
                    Console.WriteLine("{0}, ", fibonacciFirst);
                }
                else
                {
                    Console.Write("{0}, {1}, ", fibonacciFirst, fibonacciSecond);

                    BigInteger fibonacciN = 1;
                    for (int i = 3; i <= numN; i++)
                    {
                        fibonacciN = fibonacciFirst + fibonacciSecond;
                        Console.Write("{0}, ", fibonacciN);
                        fibonacciFirst = fibonacciSecond;
                        fibonacciSecond = fibonacciN;
                    }
                }
            }
        }
        Console.ReadLine();
    }
}