using System;

namespace Test
{
    class Program
    {

        /// <summary>
        /// 判断素数
        /// </summary>
        /// <param name="n"></param>
        /// <returns></returns>
        static bool IsPrime(int n)
        {
            int j = (int)Math.Ceiling(Math.Sqrt(Convert.ToDouble(n)));
            bool intFlag = true;
            for (int i = 1; i <= j; i++)
            {
                if (n % i == 0 && (i != 1) && (i != n))
                {
                    intFlag = false;
                    break;
                }
            }
            return intFlag;

        }
        /// <summary>
        /// 输入一个数判断是否符合哥德巴赫猜想
        /// 大于6的偶数都可以表示成为两个素数之和
        /// </summary>
        /// <param name="n"></param>
        /// <returns></returns>
        static bool IsGDBHArish(int n)
        {
            bool isG = false;
            if (n % 2 == 0 && n > 6)
            {
                for (int i = 1; i < n / 2; i++)
                {
                    bool b1 = IsPrime(i);
                    bool b2 = IsPrime(n - i);
                    if (b1 & b2)
                    {
                        Console.WriteLine("{0}={1}+{2}", n, i, n - i);
                        isG = true;
                    }

                }
            }
            return isG;
        }

       

        static void Main(string[] args)
        {
            //////素数
            int n = 1;

            while (n != -1)
            {
                Console.WriteLine("请输入一个数：");

                if (Int32.TryParse(Console.ReadLine(), out n))
                {
                    if (n == -1)
                        break;
                    //if (Program.IsPrime(n))
                    //{
                    //    Console.WriteLine("{0}是素数", n);
                    //}
                    //else
                    //{
                    //    Console.WriteLine("{0}不是素数", n);
                    //}

                    IsGDBHArish(n);
                }
                
            }


            Console.ReadLine();
        }
    }
}