import Data.Char (digitToInt)

dSum :: Integral a => [a] -> [a]
dSum xs = zipWith f (tail xs) (init xs)
    where
        f x y = let z = x + y in z `div` 10 + z `mod` 10

calc :: Integral a => [a] -> a
calc [] = error "Empty list"
calc [x] = x
calc xs = calc $ dSum xs

main :: IO ()
main = do
    _ <- getLine
    interact $ unlines . fmap (show . calc . fmap digitToInt) . lines