03.Programmer DNA

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Numerics;
using System.Threading.Tasks;

class ProgrammerDNA
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        char letter = char.Parse(Console.ReadLine());
        char[] letters = { 'A', 'B', 'C', 'D', 'E', 'F', 'G' };
        int dots = 3;
        int letterIndex = 0;
        if(letter == 'A')
        {
            letterIndex = 0;
        }
        else if (letter == 'B')
        {
            letterIndex = 1;
        }
        else if (letter == 'C')
        {
            letterIndex = 2;
        }
        else if (letter == 'D')
        {
            letterIndex = 3;
        }
        else if (letter == 'E')
        {
            letterIndex = 4;
        }
        else if (letter == 'F')
        {
            letterIndex = 5;
        }
        else if (letter == 'G')
        {
            letterIndex = 6;
        }
        bool increasing = true;
        for(int i = 0;i<n;i++)
        {
            Console.Write(new string('.', dots));
            for (int p = 0; p < 7 - dots * 2;p++)
            {
                Console.Write(letters[letterIndex]);
                if (letterIndex < 6)
                {
                    letterIndex++;
                }
                else if (letterIndex == 6)
                {
                    letterIndex = 0;
                }
            }
                Console.Write(new string('.', dots));
                Console.WriteLine();
            if(increasing && dots>0)
            {
                dots--;
            }
            else if(increasing && dots==0)
            {
                increasing = false;
                dots++;
            }
            else if(!increasing && dots<3)
            {
                dots++;
            }
            else if(!increasing && dots == 3)
            {
                increasing = true;
            }
        }
    }
}