Pile of cubes

pileOfCubes.hs

findNb :: Integer -> Integer
findNb m =
  if (volume == m) then       
    fromIntegral $ length cubes
  else
    -1
  where 
    cubes = listCubesTillVolume m
    volume = last cubes

listCubesTillVolume :: Integer -> [Integer]
listCubesTillVolume m =
  takeWhile (<= m) $ listCubes

listCubes :: [Integer]
listCubes =
  scanl (\acc v -> acc+v^3) 1 $ 
    iterate (+1) 2