def max(a,b); (a <=> b) >= 0 ? a : b; end
N, D = gets.split.map(&:to_i)

ans = (0 .. N).inject([-1,-1,-1]) do |s, b|
  a = D - 2 * b
  c = N - D + b
  if a >= 0 && b >= 0 && c >= 0
    max(s,[a,b,c])
  else
    s
  end
end

puts 'A' * ans[0] + 'B' * ans[1] + 'C' * ans[2]