using System;

public class Program

{

    public static double GetCircleArea(double r1 = -1, double r2 = -1, double t = -1)

    {

        if (r1 > 0 && r2 > 0)

        {

            return 2 * Math.PI * r1 * r2;

        }

        else if (t > 0)

        {

            return Math.PI * t * t / 8;

        }

        return -1;

    }   

    public static void Main()

    {

        Console.WriteLine("UniLecs");

        Console.WriteLine(string.Format("Answer = {0}", GetCircleArea(10, 10))); // ~628

        Console.WriteLine(string.Format("Answer = {0}", GetCircleArea(15, 20))); // ~1884

        Console.WriteLine(string.Format("Answer = {0}", GetCircleArea(t:10)));   // ~39.2

    }

}