main = getLine >> getLine >>= print . cardf . map read . words

cardf :: [Int] -> Int
cardf (n:ns) = cardf' [n] ns
 where
  cardf' s [] = maximum s
  cardf' s (0:ns) = let s' = 0:s in cardf' [maximum s', minimum s'] ns
  cardf' s (n:ns) = let s' = [(+n),(+(negate n)),(*n),(`quot` n)] <*> s in cardf' [maximum s', minimum s'] ns