main = putStrLn (show ans)

ans = indexMax (map collatz [0..10^6])

collatz :: Integer -> Int

collatz 0 = 0

collatz 1 = 1

collatz n = (collatz (if mod n 2 == 0 then (div n 2) else (n * 3 + 1))) + 1

indexMax :: [Int] -> Int

indexMax = indexMax' 0 (-1) 0

indexMax' _ j _ [] = j -- Current index, max index, max value

indexMax' i j v (x:xs) =

if (j == -1 || x > v)

then (indexMax' (i+1) i x xs)

else (indexMax' (i+1) j v xs)