SquareFrameEasierSolution

            int n = int.Parse(Console.ReadLine());

            if (n == 1)
            {
                Console.WriteLine("+");
                return;
            }

            Console.Write("+");
            for (int i = 0; i < n - 2; i++)
            {
                Console.Write(" -");
            }
            Console.WriteLine(" +");

            for (int row = 0; row < n - 2; row++)
            {
                Console.Write("|");
                for (int i = 0; i < n - 2; i++)
                {
                    Console.Write(" -");
                }
                Console.WriteLine(" |");
            }
            Console.Write("+");
            for (int i = 0; i < n - 2; i++)
            {
                Console.Write(" -");
            }
            Console.WriteLine(" +");
        }
    }
}