import Data.Map
import Data.List

foo (x : xs) = foldr (\x, y -> (cycles ! x) !! (y 'rem' 4)) (x 'rem' 10) xs
    where cycles = fromAscList [(0, [0, 0, 0, 0])
                               ,(1, [1, 1, 1, 1])
                               ,(2, [6, 2, 4, 8])
                               ,(3, [1, 3, 9, 9])
                               ,(4, [6, 4, 6, 4])
                               ,(5, [5, 5, 5, 5])
                               ,(6, [6, 6, 6, 6])
                               ,(7, [1, 7, 9, 3])
                               ,(8, [6, 8, 4, 2])
                               ,(9, [1, 9, 1, 9])]