import Data.Monoid
main = getContents >>= putStrLn . solve . map (\x -> take (length x - 2) x) . lines

solve :: [String] -> String
solve [xs, ys]
    | cond == GT = sa
    | cond == LT = sb
    | otherwise = "-1"
    where
        cond = compare la lb `mappend` comp pa pb
        comp [] [] = mempty
        comp (a : as) (b : bs) = compare a b `mappend` comp as bs
        la = length pa
        lb = length pb
        f = takeWhile (/= ' ')
        g = dropWhile (/= ' ')
        sa = f xs
        sb = f ys
        pa = g xs
        pb = g ys