#! /usr/bin/env stack
-- stack --resolver lts-12.20 --install-ghc script
module Main where

import Control.Arrow ((***))
import qualified Data.List    as L
import qualified Data.HashSet as S

main :: IO ()
main = interact $ (show .) $ (. lines) $ \codes ->
   loopRight (S.empty, L.concatMap deletions codes) $ \(seen, d:ds) ->
      if S.member d seen
      then Left  (snd d)
      else Right (S.insert d seen, ds)

loopRight :: b -> (b -> Either a b) -> a
loopRight b f = either id (`loopRight` f) (f b)

deletions :: [a] -> [(Int, [a])]
deletions []     = []
deletions (x:xs) = (0, xs) : map ((+1) *** (x:)) (deletions xs)