一列数的规则如下: 1、1、2、3、5、8、13、21、34..

Test Result：

Test Code：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace RecursiveFunctionExercise
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch watch = new Stopwatch();
            watch.Start();
            Console.WriteLine("Calculate result: " + RecusiveFunction(9));
            watch.Stop();

            Console.WriteLine("Calcualte Time: " + watch.Elapsed.TotalMilliseconds + " TotalMilliseconds");

            Console.ReadLine();
        }

        private static int RecusiveFunction(int num)
        {
            if (num <= 0)
            {
                return 0;
            }
            if (num > 0 && num <= 2)
            {
                return 1;
            }

            return RecusiveFunction(num - 2) + RecusiveFunction(num - 1);
        }
    }
}