input: def encode_rotational(s: str):
      """
      returns a string encoded by rotating groups of three characters.
      """
      # Break string into groups. Each containing 3 characters.
      groups = [s[(3 * i):min((3 * i + 3), len(s))] for i in range((len(s) + 2) // 3)]
      # Rotate elements in each group. Only if group size is 3 characters.
      groups = [(group[1:] + group[0]) if len(group) == 3 else group for group in groups]
      return "".join(groups)
  
  
  def decode_rotational(s: str):
      """
      accepts a string encoded by encode_rotational function. Returns the original string.
      """
output:     # Break string into groups. Each containing 3 characters.
      groups = [s[(3 * i):min((3 * i + 3), len(s))] for i in range((len(s) + 2) // 3)]
      # Rotate elements in each group to the left to the original position. Only if group size is 3 characters.
      groups = [(group[-1] + group[:-1]) if len(group) == 3 else group for group in groups]
      return "".join(groups)