using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string code = "R2222AB";

        char lastChar = code[^1];

        char penultimateChar = code[^2];

        if (lastChar is >= 'A' and < 'Z')

        {

            lastChar++;

        }

        else if (lastChar is 'Z')

        {

            lastChar = 'A';

        }

        if (lastChar is 'Z' && penultimateChar < 'Z')

        {

            penultimateChar++;

        }

        else if (penultimateChar is 'Z')

        {

            throw new System.InvalidOperationException("Limite atingido!");

        }

        Console.WriteLine(code);

        code = code[..^2] + penultimateChar + lastChar;

        Console.WriteLine(code);        

    }

}