using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;



namespace Excise_1

{

    class Program

    {

        static void Main(string[] args)

        {

            int i, r, k, m;

            string inputStr;

            Console.WriteLine("请输入一个数：");

            try {

                do

                {

                    inputStr = Console.ReadLine();

                    m = Convert.ToInt32(inputStr);

                }

                while (m < 2);

                try

                {

                    i = 2; k = m / 2;

                    while (i <= k)

                    {

                        r = m % i;

                        if (r == 0) break;

              &