for循环语句之兔子生崽

有一对幼兔，幼兔经过一个月长为小兔，小兔经过一个月长为大兔并且生下一对幼兔，而且大兔每月还会生下一对幼兔，问N个月后有多少对兔子

            Console.WriteLine("请输入经过了几个月：");
            int n = Convert.ToInt32(Console.ReadLine());

            int syt = , byt = ;
            int sxt = , bxt = ;
            int sdt = , bdt = ;

            for (int i = ; i <= n; i++)
            {
                byt = sdt + sxt;
                bxt = syt;
                bdt = sdt + sxt;

                syt = byt;
                sxt = bxt;
                sdt = bdt;
            }

            Console.WriteLine("经过" + n + "个月后：");
            Console.WriteLine("幼兔为：" + byt + "对");
            Console.WriteLine("小兔为：" + bxt + "对");
            Console.WriteLine("大兔为：" + bdt + "对");
            int sum = byt + bxt + bdt;
            Console.WriteLine("兔子总共有：" + sum + "对");

            Console.WriteLine("兔子总共有：{0}对,小兔子有{1}对", sum, bxt);