Найти площадь треугольника — С#

class Program
{
    public class Tochka
    {
        public double x, y;
        // два конструктора 
        public Tochka() { }
        public Tochka(double x, double y)
        {
            this.x = x;
            this.y = y;
        }
    }

    static double Distance(Tochka p1, Tochka p2)
    {
        return Math.Sqrt(Math.Pow(p2.x - p1.x, 2) +
                         Math.Pow(p2.y - p1.y, 2));
    }
    static double Surface(Tochka p1, Tochka p2,
        Tochka p3)
    {
        double a = Distance(p1, p2);
        double b = Distance(p2, p3);
        double c = Distance(p1, p3);
        double p = (a + b + c) / 2;
        return Math.Sqrt(p * (p - a) * (p - b) * (p - c));
    }

    static void Main(string[] args)
    {
        Tochka p1 = new Tochka();
        Console.Write("p1.x = ");
        p1.x = Convert.ToDouble(Console.ReadLine());
        Console.Write("p1.y = ");
        p1.y = Convert.ToDouble(Console.ReadLine());


        Tochka p2 = new Tochka();
        Console.Write("p2.x = ");
        p2.x = Convert.ToDouble(Console.ReadLine());
        Console.Write("p2.y = ");
        p2.y = Convert.ToDouble(Console.ReadLine());

        Tochka p3 = new Tochka();
        Console.Write("p3.x = ");
        p3.x = Convert.ToDouble(Console.ReadLine());
        Console.Write("p3.y = ");
        p3.y = Convert.ToDouble(Console.ReadLine());
        Console.WriteLine("S = {0}", Surface(p1, p2, p3));
        Console.ReadKey();
    }
}