using System;

public abstract class Shape

{

    public double height;

    public double width;

    public abstract double calculateSurface();

    public Shape(double height, double width)

    {

        this.height = height;

        this.width = width;

    }

}

public class Triangle : Shapea

{

    public Triangle(double height, double width) : base (height, width)

    {}

    public override double calculateSurface()

    {

        return height*width/2;

    }

}