public static ulong Fibonacci(int n)
        {
            ulong a = 0;
            ulong b = 1;
            // In N steps compute Fibonacci sequence iteratively.
            Stopwatch stopWatch = new Stopwatch();
            stopWatch.Start();
            for (int i = 0; i < n; i++)
            {
                ulong temp = a;
                a = b;
                b = temp + b;
            }
            stopWatch.Stop();
            // Get the elapsed time as a TimeSpan value.
            TimeSpan ts = stopWatch.Elapsed;
            string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}",
                ts.Hours, ts.Minutes, ts.Seconds,
                ts.Milliseconds / 10);
            //Console.WriteLine("Elapsed time:" + elapsedTime);
            return a;
        }
        static void Main(string[] args)
        {
            var i = 95;
            Console.WriteLine(Fibonacci(i) + ":   " + i);
            Console.Read();
        }