static void Main(string[] args)
{
Triangle tri = new Triangle();
tri.basen = 3;
tri.height = 4;
Console.WriteLine("Triangle area = " + tri.Area());
Circle cir = new Circle();
cir.radius = 5;
Console.WriteLine("Circle area = " + cir.Area());
Rectangle rec = new Rectangle();
rec.height = 5;
rec.width = 4;
Console.WriteLine("Rectangle area = " + rec.Area());
Square squ = new Square();
squ.width = 6;
Console.WriteLine("Square area = " + squ.Area());
Console.ReadKey();
}