Square of Stars

using System;

    class Program
    {
        static void Main()
        {
            var arr =int.Parse(Console.ReadLine());
            for (var i = 0; i < arr; i++)
            {
                var output = "";
                for (var j = 0; j < arr; j++)
                {
                    if (i == 0 || i == arr - 1 || j == 0 || j == arr - 1)
                    {
                        output += "*";
                    }
                    else
                    {
                        output += " ";
                    }
                }
                Console.WriteLine(output);
            }
        }
    }