#include <iostream>
    using namespace std;
    class FirstClass
    {
        protected:
        int width, height;
        public:
        void set_values (int x, int y)
        {
            width = x; height = y; 
        }
        virtual int area (void) = 0;
    };
    class SecondClass: public FirstClass
    {
        public:
        int area (void)
        { 
            return (width * height);
        }
    };
    class ThirdClass: public FirstClass 
    {
        public:
        int area (void)
        {
            return (width * height / 2); 
        }
    };
    int main () 
    {
        SecondClass Rectangle;
        ThirdClass trgl;
        FirstClass * ppoly1 = &Rectangle;
        FirstClass * ppoly2 = &trgl;
        ppoly1->set_values (3, 6);
        ppoly2->set_values (3, 6);
        cout << ppoly1 -> area() <<" ";
        cout << ppoly2 -> area();
        return 0;
    }