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

loopRight :: b -> (b -> Either a b) -> a
loopRight b f = case f b of
   Left  a  -> a
   Right b' -> loopRight b' f

main :: IO ()
main = interact $ show . \input ->
   let codes = lines input :: [[Char]]
   in loopRight ([], codes) $ \(seen, c:cs) ->
         case filter (`isSimilarTo` c) seen of
            []    -> Right (c:seen, cs)
            (x:_) -> Left (c, x, foldMap (\(a,b) -> if a == b then [a] else [])
                                         (zip c x))

isSimilarTo :: (Eq a) => [a] -> [a] -> Bool
(x:xs) `isSimilarTo` (y:ys)
   | x == y    = xs `isSimilarTo` ys
   | otherwise = xs == ys
_ `isSimilarTo` _ = False