import Control.Applicative ((<$>), (<*>))
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as B

main :: IO ()
main = do
  solve <$> getl B.words <*> getl B.words >>= B.putStrLn

solve :: [ByteString] -> [ByteString] -> ByteString
solve [sa, pa, _] [sb, pb, _]
  | la > lb = sa
  | la < lb = sb
  | otherwise = f pa pb
    where
      la = B.length pa
      lb = B.length pb
      f a b | B.null a = B.pack "-1"
            | B.head a > B.head b = sa
            | B.head a < B.head b = sb
            | otherwise = f (B.tail a) (B.tail b)

getl :: (ByteString -> a) -> IO a
getl f = f <$> B.getLine