using System;  

    using System.Collections.Generic;  

    using System.Linq;  

    using System.Text;  

    namespace ConsoleApplication13

    {  

       public abstract class mcn 

        {  

            public abstract  int addi(int b, int a) ;

​

        }  

        public class mcn1: mcn 

        {  

            public    override int  addi(int a,int b)

            {

                Console.WriteLine("a="+a+"\nb="+b);

            }

            public int mul(int a, int b) 

            {  

                return a * b;  

            } 

        }  

        public class test 

        {  

            public static void Main(string[] args) 

            {  

                mcn1 ob = new mcn1();  

                int result = ob.addi(5, 10);  

                Console.WriteLine("the result is {0}", result);  

            }  

        }  

    }