using System;

namespace Application {

    // Base class Cost

    public class Shape {

        public void setSide(int s) {

            side = s;

        }

        protected int side;

    }

    //interface

    public interface Cost {

        int getCost(int area);

    }

    // Derived class, using Interface and Base class

    class square: Shape, Cost {

        //methods in derived class

        public int getArea() {

            return (side * side);

        }

        public int getCost(int area) {

            return area * 10;

        }

    }

    public class SquareInheritance {

        public static void Main(string[] args) {

            square sq = new square();

            int area;

            sq.setSide(5);

            area = sq.getArea();

​

            // Print the area of the object.

            Console.WriteLine("The area is: {0}", sq.getArea());

            Console.WriteLine("The cost is: {0}", sq.getCost(area));

        }

    }

}