using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var ra = new int[5]{2,3,4,5,6};

        Console.WriteLine(TotalAllEvenNumbers(ra));

        var mycircle = new Circle();

        var rr = mycircle.Calculate(r => r * Math.PI * r);

        Console.WriteLine(rr);

    }

    static long TotalAllEvenNumbers(int[] intArray) {

        return intArray.Where(i => i % 2 == 0).Sum(i => (long)i);

    }

}

​

public sealed class Circle {

  private double radius = 5.0;

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

    return op(radius);

  }

}