Figure Area

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Area_of_Figures
{
    class Program
    {
        static void Main(string[] args)
        {
            string figure = Console.ReadLine();
            double a = double.Parse(Console.ReadLine());
            var square = (a * a);
            var circle = Math.PI*(a * a);
            if (figure == "square")
            {
                Console.WriteLine(square);
            }
            else if (figure == "circle")
            {
                Console.WriteLine(circle);
            }
            double b = double.Parse(Console.ReadLine());
            var rectangle = (a * b);
            var triangle = (a * b) / 2;
            if (figure == "rectangle")
            {
                Console.WriteLine(rectangle);
            }
            else if (figure == "triangle")
            {
                Console.WriteLine(rectangle);
            }
        }
    }
}