newtype FourSeven = FourSeven Integer

instance Eq FourSeven where
	(FourSeven x) == (FourSeven y) = x == y

instance Ord FourSeven where
	(FourSeven x) `compare` (FourSeven y)
		| x == y = EQ
		| length x' > length y' = GT
		| length x' < length y' = LT
		| otherwise = foldl (****) EQ (zipWith cmp x' y')
		where x' = numToList x;
			  y' = numToList y;


(****) :: Ordering -> Ordering -> Ordering
(****) GT _ = GT
(****) LT _ = LT
(****) EQ x = x

cmp :: Integer -> Integer -> Ordering
cmp x y
	| x == y = EQ
	| (x /= 4 && x /= 7) || (y /= 4 && y /= 7) = x `compare` y
	| x == 4 && y == 7 = GT
	| x == 7 && y == 4 = LT
	| otherwise = EQ

numToList :: Integer -> [Integer]
numToList 0 = []
numToList n = numToList (n `div` 10) ++ [(n `mod` 10)]

main = do
	[a, b] <- getLine >>= return . map read . words
	print $
		if FourSeven a < FourSeven b
			then b
			else a