{-# LANGUAGE OverloadedLists #-}
{-# LANGUAGE OverloadedStrings #-}

import qualified Data.ByteString.Char8 as B
import qualified Data.Set              as S

main :: IO ()
main = solve <$> readParams >>= B.putStrLn

readParams :: IO [B.ByteString]
readParams = B.words <$> B.getContents

solve :: [B.ByteString] -> B.ByteString
solve = S.elemAt 0 . (["1","2","3"] S.\\) . S.fromList
