//求5！+ 4！+3！ +2！ +1！

 long A = 0;
            for (int i = 1; i <= 1000; i++)
            {
                long z = 1; int j = i; while (j > 0)
                {
                    z *= j; j--;
                }
                A += z;
            }
             Console.Write("结果：" + A + System.Environment.NewLine);

//求100以内的素数

            int i = 1;
            bool s;
            for (; i < 100; i++)
            {
                s = true;
                for (int j = 2; j < i; j++)
                {
                    if (i % j == 0)
                        s = false;
                }
                if (s)
                    Console.WriteLine(i.ToString());

            //执行任务问题
            for (int A = 0; A <= 1; A++)
                for (int B = 0; B <= 1; B++)
                    for (int C = 0; C <= 1; C++)
                        for (int D = 0; D <= 1; D++)
                            for (int E = 0; E <= 1; E++)
                                for (int F = 0; F <= 1;F++ )
                                {
                                    if (A + B > 0 && A + D <= 1 && A + E + F == 2 && B + C >= 1 && C + D == 1)
                                   
                                        if (D == 0 && E + D == 0)
                                        {
                                         Console.WriteLine("A="+A+"   B="+B+"    C="+C+"   D="+D+"   E="+E+"   F="+F+"");
                                        }
                                       
                                        else if (D ==1&&D+E>=1)
                                       
                                   
                                    {
                                        Console.WriteLine("A="+A+"   B="+B+"    C="+C+"   D="+D+"   E="+E+"   F="+F+"");
                                    }
                                }

             //百鸡百钱   x = 公鸡 y = 母鸡  z =小鸡
            for (int x = 1; x < 50; x++)
                for (int y = 1; y < 100; y++)
                    for (int z = 2; z < 100; z++)
                    {
                        if (x * 2 + y * 1 + z * 0.5 == 100 && x + y + z == 100)
                        {
                            Console.WriteLine("公鸡"+x+"只，母鸡"+y+"只，小鸡"+z+"只");
                        }
                    }