using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Ch04Ex06
{
class Program
    {
static void Main(string[] args)
        {
double x, y;

for (x = -50; x <= 50; x+=2)
            {
for (y = -50; y <= 50; y+=2)
                {
if ((x * x + y * y) > 500 || (x * x + y * y) < 400)
                    {
if (x == 0 || y == 0)
                            Console.Write("");
else
                        {
                            Console.Write("□");
                        }

                    }
else
                        Console.Write("");
                }
                Console.WriteLine();
            }
Console.ReadKey();


        }
    }
}