1,1,2,3,5,8,13,21,34.....的递归算法

 public static int Foo(int i)
        {
            if (i <= 0)
                return 0;
            else if (i > 0 && i <= 2)
                return 1;
            else return Foo(i - 1) + Foo(i - 2);
        }
        static void Main(string[] args)
        {
            Console.WriteLine ( Foo(30));
            Console.ReadKey();
        }