module Main where

import Data.List (group)

type Input  = [Char]
type Output = String

parse :: String -> Input
parse = head . lines

solve :: Input -> Output
solve =
    flip take (repeat 'a')
    . succ
    . maximum
    . map length
    . (\list -> if null list then [[]] else list)
    . filter ((== 'a') . head)
    . group

render :: Output -> String
render = id

main :: IO ()
main =
    interact
        ( render
        . solve
        . parse
        )