import Data.Ord (comparing)
import Data.List (maximumBy)

main :: IO ()
main = putStr $ show $ fst $ maximumBy (comparing snd) $ zip range $ map collatz range
  where
    range :: [ Int ]
    range = [1 .. 10 ^ 6 - 1]

-- eh 12s isn't much
collatz :: Int -> Int
collatz n
  | n == 1 = 1
  | even n = 1 + collatz (div n 2)
  | otherwise = 1 + collatz (3 * n + 1)