Primer término Fibonacci con 1000 o más cifras (C#)

using System;
using System.Diagnostics;
using System.Numerics;

namespace Desafio
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch myTimer = Stopwatch.StartNew();

            BigInteger fib1 = BigInteger.One;
            BigInteger fib2 = BigInteger.One;
            BigInteger fib3 = fib1 + fib2;
            int count = 3;
            BigInteger maxNumber = BigInteger.Pow((BigInteger)10, 999);
            while (fib3 < maxNumber)
            {
                fib1 = fib2;
                fib2 = fib3;
                fib3 = fib1 + fib2;
                ++count;
            }
            myTimer.Stop();

            Console.WriteLine("{0}", count);
            Console.WriteLine("{0}", fib3);

            Console.WriteLine("{0} nanosegundos", (double)myTimer.ElapsedTicks / 10);
        }
    }
}