import Data.Maybe
import Data.List
import qualified Data.ByteString.Char8 as BS
import Data.Char


digitsum :: Integer -> Integer
digitsum n
  | n < 10 = n
  | otherwise = n `mod` 10 + digitsum (n `div` 10)


g n
  | n < 10 = n
  | otherwise = g (digitsum n)


main = do
  n <- readLn :: IO Int
  p <- foldl1 (*) . map (fst . fromJust . BS.readInteger) . BS.words <$> BS.getLine :: IO Integer

  print $ g p