s = gets.not_nil!.chomp
d = 1
result = String.build do |str|
  s.each_char do |c|
    current = c.ord - 'A'.ord
    new_char = (current - d + 26) % 26 + 'A'.ord
    str << new_char.chr
    d = (d + 1) % 26
  end
end
puts result