class Program

    {

        //第一种（1-2）+（3-4）+（5-6）...+m

        public static void Test(int m) {

            int z = ;

            if (m %  == )

            {

                z = -(m / );

            }

            else {

                z = -(m -) /   + m;

            }

            Console.WriteLine(z);

        }

        //第二种1+(-2+3)+(-4+5)+(-6+7)...+m

        public static void Test1(int m) {

            int z = ;

            if (m%==) {

                z = (m - ) / +-m;

            }

            else {

                z = (m - ) /  + ;

            }

            Console.WriteLine(z);

        }

        static void Main(string[] args)

        {

            //第三种

            int z = ;

            for (var i = ; i < ; i++)

            {

                if (i %  == )

                {

                    z += i;

                }

                else

                {

                    z += -i;

                }

            }

            Test();

            Test1();

            Console.WriteLine(z);

            Console.ReadLine();

        }

    }