Exam July Morning 3. Panda Scotland Flag

using System;

public class PandaScotlandFlag
{
    public static void Main()
    {
        checked
        {
            int length = int.Parse(Console.ReadLine());

            char letter = 'A';
            if (length > 1)
            {
                int innerWidth = length - 2;
                string innerTopSequence = new string('#', innerWidth);
                int counter = 1;
                Console.WriteLine("{0}{1}{2}", letter, innerTopSequence, (char)(letter + counter));
                string outerSequence;
                string innerSequence;
                char firstLetter;
                char secondLetter;
                for (int row = 1; row < (length / 2); row++)
                {
                    innerWidth -= 2;
                    counter++;
                    outerSequence = new string('~', row);
                    innerSequence = new string('#', innerWidth);
                    firstLetter = (char)(letter + (counter % 26));
                    counter++;
                    secondLetter = (char)(letter + (counter % 26));
                    Console.WriteLine("{0}{1}{2}{3}{0}", outerSequence, firstLetter, innerSequence, secondLetter);
                }

                string outerHyphenSeq = new string('-', length / 2);
                counter++;
                char middleLetter = (char)(letter + (counter % 26));
                Console.WriteLine("{0}{1}{0}", outerHyphenSeq, middleLetter);
                int outerWidth = (length / 2) - 1;
                innerWidth = 1;
                for (int row = 0; row < (length / 2); row++)
                {
                    outerSequence = new string('~', outerWidth);
                    innerSequence = new string('#', innerWidth);
                    counter++;
                    firstLetter = (char)(letter + (counter % 26));
                    counter++;
                    secondLetter = (char)(letter + (counter % 26));
                    Console.WriteLine("{0}{1}{2}{3}{0}", outerSequence, firstLetter, innerSequence, secondLetter);
                    outerWidth--;
                    innerWidth += 2;
                }
            }
            else
            {
                Console.WriteLine(letter);
            }
        }
    }
}