main = getLine >>= putStrLn . hole . map read . words

hole [n,d]
 | n < d = replicate (n-(d-n)) 'A' ++ replicate (d-n) 'B'
 | n > d = replicate (n-(n-d)) 'A' ++ replicate (n-d) 'C'
 | otherwise = replicate n 'A'