# Pastebin RtaAP8sh
gamenst :: Int -> [Int] -> Int
gamenst nth inp = runST $ do
  prevs <- MV.replicate nth (-1)
  traverse_ (uncurry (MV.write prevs)) (zip inp [1..])
  foldM (\n pos -> do
            p <- MV.unsafeRead prevs n
            MV.unsafeWrite prevs n pos
            pure (pos - if p == -1 then pos else p)) 0 [length inp + 1 .. nth - 1]