Area of Figures (square,rectangle,circle,triangle)

using System;

class Program
{
    static void Main(string[] args)
    {
        string figure = Console.ReadLine();
        if(figure=="square")
        {
            double d = double.Parse(Console.ReadLine());
            double s = Math.Round(d * d, 3);
            Console.WriteLine(s);

        }
        else if (figure == "rectangle")
        {
            double w = double.Parse(Console.ReadLine());
            double h = double.Parse(Console.ReadLine());
            double a = Math.Round(w * h, 3);
            Console.WriteLine(a);
        }
        else if (figure == "circle")
        {
            double r = double.Parse(Console.ReadLine());
            double s = Math.Round(Math.PI*r*r,3);
            Console.WriteLine(s);
        }
        else if (figure == "triangle")
        {
            double w = double.Parse(Console.ReadLine());
            double h = double.Parse(Console.ReadLine());
            double s = Math.Round(w*h/2,3);
            Console.WriteLine(s);
        }
    }
}