using System;

public class Program

{

    public interface ICalculator

    {

        int Add(int a, int b);

        int Subtract(int a, int b);

        int Multiply(int a, int b);

        int Divide(int a, int b);

    }

​

    public class Calculator : ICalculator

    {

        int ICalculator.Add(int a, int b)

        {

            return a + b;

        }

​

        int ICalculator.Subtract(int a, int b)

        {

            return a - b;

        }

​

        int ICalculator.Multiply(int a, int b)

        {

            return a * b;

        }

​

        int ICalculator.Divide(int a, int b)

        {

            return a / b;

        }

    }

    public static void Main()

    {

        // Since the Interface is implemented explicitly

        // it does NOT even compile.

        Calculator calculator = new Calculator();

        //int res = calculator.Add(20, 50);

​

        // Object type interface should be used

        ICalculator calc = new Calculator();

        int value = calc.Add(20, 30);

        Console.WriteLine(value);

    }

}