using System;

public class Program

{

    public static void Main()

    {

        Console.Write("Enter Number - 1 :- ");

        int number1 = Convert.ToInt32(Console.ReadLine());

        Console.Write("Enter Number - 2 :- ");

        int number2 = Convert.ToInt32(Console.ReadLine());

        Console.Write("Enter Number - 3:- ");

        int number3= Convert.ToInt32(Console.ReadLine());

        Calculate c1 = new Calculate();

        c1.sumOfTwo(number1, number2);

        c1.sumOfThree(number1, number2, number3);

    }

}

​

abstract class Sum {

    abstract public void sumOfTwo(int number1, int number2);

    abstract public void sumOfThree(int number1, int number2, int number3);

}

​

class Calculate : Sum {

    public override void sumOfTwo(int no1, int no2){

        Console.Write("\n\nAddition of {0} and {1} is {2}", no1, no2, (no1 + no2));

    }

    public override void sumOfThree(int no1, int no2, int no3) {

        Console.Write("\n\nAddition of {0}, {1} and {2} is {3}", no1, no2, no3, (no1 + no2 + no3));

    }

}