import Data.Char

strToNum' :: String -> Integer
strToNum' [] = 0
strToNum' (x:xs)
	| x == '4' = 7 + 10 * strToNum' xs
	| x == '7' = 4 + 10 * strToNum' xs
	| otherwise = fromIntegral (ord x - ord '0') + 10 * strToNum' xs

strToNum = strToNum' . reverse

main = do
	[a, b] <- getLine >>= return . words
	print $ maximum [strToNum a, strToNum b]