How to find area & volume of different shapes with C#?

using System;

interface Shape{
  double Area{get;}
  string Desc{get;}
};

interface TwoDimensionalShape : Shape {}

interface ThreeDimensionalShape : Shape {
  double Volume{get;}
}

class Circle: TwoDimensionalShape{
  private double Radius;
  public Circle(double r){Radius = r;}
  public double Area{ get{ return ((Radius * Radius) * Math.PI); }}
  public string Desc{get{return "A circle";}}
}

class Square: TwoDimensionalShape{
  private double Side;
  public Square(double s){Side = s;}
  public double Area{ get{ return (Side * Side); }}
  public string Desc{get{return "A square";}}
}
class Sphere: ThreeDimensionalShape{
  private double Radius;
  public Sphere(double r){Radius = r;}
  public double Area{ get{ return (4 * Math.Pow(Radius,2) * Math.PI); }}
  public double Volume{ get{ return (4/3.0 * Math.Pow(Radius,3) * Math.PI); }}
  public string Desc{get{return "A sphere";}}
}

class Cube: ThreeDimensionalShape{
  private double Side;
  public Cube(double s){Side = s;}
  public double Area{ get{ return (6*(Side * Side)); }}
  public double Volume{ get{ return Math.Pow(Side,3);}}
  public string Desc{get{return "A cube";}}
}

class TestShapes{
  public static void Main(string[]args){
    Shape[]shapes={new Circle(3.5), new Cube(6.2), new Sphere(4.7), new Square(7.8)};
    ThreeDimensionalShape s3;
    foreach(Shape s in shapes){
      Console.WriteLine("Shape is: {0}", s.Desc);
      if(s is TwoDimensionalShape){
        Console.WriteLine("Area is: {0:0.00}", (s as TwoDimensionalShape).Area);
        continue;
      }
      if(s is ThreeDimensionalShape){
        s3 = s as ThreeDimensionalShape;
        Console.WriteLine("Area is: {0:0.00}", s3.Area);
        Console.WriteLine("Volume is: {0:0.00}", s3.Volume);
      }
    }
  }
}

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