splitlist :: [a] -> ([a],[a])
splitlist list = (take n list,drop n list)
  where n = (length list) `div` 2

inBoth :: (Eq a) => ([a],[a]) -> [a]
inBoth (first,second) = do
  inFirst <- first
  if (inFirst `elem` second) then return inFirst else []



main = do
  input <- readFile "three-input.txt"
  print $ map ( inBoth . splitlist ) $ lines input