import Control.Monad.Identity
import Control.Monad.State
import System.Environment

type M = StateT Char Identity

main = do [x] <- getArgs
          print $ head $ runIdentity $ evalStateT (f $ read x) 'a'

f :: Int -> M [Char]
f 0 = return []
f (n+1) = do st <- get
             rest <- f n
             return (st:rest)