函数求羊

class Program
    {
        public int yang(int cun)     //求的羊的数量      已知的是村的个数
        {
            int sum = 0;
            for (int i = 7; i>=cun ; i--)
            {
                if (i==7)
                {
                    sum = 2;
                }
                else
                {
                    sum = (2 * (sum + 1));
                }
            }
            return sum;
        }
        static void Main(string[] args)
        {
            Console.WriteLine(new Program().yang(0));
            Console.ReadLine();
        }
    }