using System;

using System.Collections.Generic;

using System.Collections.Generic;

public class Program

{

    public class Circle

    {

        private double radius;

        public Circle(double radius)

        {

            this.radius = radius;

        }

        public double Calculate(Func<double, double> function)

        {

            return function(radius);

        }

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        List<Circle> circles = new List<Circle>()

            { new Circle(1), new Circle(2), new Circle(1.5), new Circle(11) };

    }

}

​