import Control.Applicative ((<$>))

main :: IO ()
main = solve <$> words <$> getLine >>= putStrLn

solve :: [String] -> String
solve [a, b] | al > bl = a
             | al < bl = b
             | otherwise = case foldr f EQ (zip a b) of
                            GT -> a
                            _ -> b
  where al = length a
        bl = length b
        f (x, y) b = case comp x y of
                      EQ -> b
                      GT -> GT
                      LT -> LT

comp :: Char -> Char -> Ordering
comp '4' '7' = GT
comp '7' '4' = LT
comp x y = compare x y