[ Telerik C#] LOOPS - EX 7

/* Write a program that reads a number N and calculates the sum of the first N members
 * of the sequence of Fibonacci: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, …
 * Each member of the Fibonacci sequence (except the first two) is a sum of the previous two members.
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ex7
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter N: ");
            ulong n = ulong.Parse(Console.ReadLine());

            ulong firstN = 1;
            ulong secondN = 0;
            ulong thirdN = 0;
            ulong sum = 0;

            for (ulong i = 0; i <= n; i++)
            {
                thirdN = firstN + secondN;
                firstN = secondN;
                secondN = thirdN;
                Console.WriteLine("{0} : = {1}", i, thirdN);
                sum += thirdN;
            }
            Console.WriteLine("Sum is : {0}" ,sum);
        }
    }
}