Hi, I am trying to solve this problem: https://www.spoj.pl/problems/LASTDIG/ It is very simple. Given a and b, return the last digit of a^b. b could be large, so I used logarithmic exponentiation and wrote/submitted the code below for this problem: ---------------------------------------------------------------------- lastdigit :: Int -> Int -> Int -> Int lastdigit 0 0 _ = 1 lastdigit a b c | even b = lastdigit ( (a*a) `rem` 10 ) (b `quot` 2) c | b == 1 = (a*c) `rem` 10 | otherwise = lastdigit ( (a*a) `rem` 10 ) (b `quot` 2) (a*c) doit :: [Char] -> Int doit line = lastdigit (read $ head $ words line) (read $ last $ words line) 1 main = do n <- getLine inputs <- sequence $ take (read n) $ repeat getLine let slist = map doit inputs mapM_ (putStrLn.show) slist ------------------------------------------------------------------- As n in main is at most 30, I thought this would easily run in 1 second, but I get a time limit exceeded error on the site. Can someone tell me where my code is taking too much time? Thanks in advance! -- Aditya Manthramurthy