using System;

public sealed class Circle {

  private double _radius;

  public Circle(double radius)

  {

      _radius = radius;

  }

  public double Calculate(Func<double, double> op) {

    return op(_radius);

  }

}

​

public class Program

{

    public static void Main()

    {

        int radius = 5;

        int circumference = 0;

        //TODO - Please fix this!!

        Console.WriteLine("The circumference of a circle with Radius = {0} is {1}", radius, circumference);

    }

}