using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication48
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Shape> ShapeList = new List<Shape>();

            Shape square1 = new Square(4);
            ShapeList.Add(square1);

            Shape circle1 = new Circle(3);
            ShapeList.Add(circle1);

            Shape triangle1 = new Triangle(6, 8);
            ShapeList.Add(triangle1);

            foreach (Shape item in ShapeList)
            {
                Console.WriteLine(item.GetSquare());
            }
        }
    }

    abstract class Shape
    {
        public abstract int GetSquare();
    }

    class Square : Shape
    {
        int len;
        public Square(int l)
        {
            len = l;
        }
        public override int GetSquare()
        {
            return len * len;
        }
    }

    class Circle : Shape
    {
        int radius;

        public Circle(int r)
        {
            radius = r;
        }
        public override int GetSquare()
        {
            return (int)Math.PI * radius * radius;
        }

    }

    class Triangle : Shape
    {
        int foundation, height;

        public Triangle(int f, int h)
        {
            foundation = f;
            height = h;
        }
        public override int GetSquare()
        {
            return foundation * height / 2;
        }
    }
}