public class Abstract {
  public static void main(String[] args) {
    Shape[] data = { new Rectangle(3,2), new Square(3)};
    for (int i=0; i < data.length; i++)
      System.out.println(data[i].getArea()); 
  }
}

abstract class Shape {
  public abstract double getArea(); 
}

abstract class Quadrilateral extends Shape {
  protected double s1,s2,s3,s4;
  public Quadrilateral(double s1, double s2, double s3, double s4) {
    this.s1=s1; this.s2=s2; this.s3=s3; this.s4=s4;
  }
}

abstract class Triangle extends Shape { }

class Rectangle extends Quadrilateral {
  public Rectangle(double s1, double s2) {
    super(s1,s2,s1,s2);
  }
  public double getArea() { return s1*s2; }
}
class Square extends Rectangle { 
  public Square(double s) {
    super(s,s);
  }
}