def quizn_to_index(quizn):
  """See: https://github.com/fielddaylab/jo_wilder/blob/master/src/scenes/quiz.js

  For some reason there are 5 quizzes, but there is no quiz numbered 1.
  
  Returns:
    The correct quiz number for quizzes 2-5, or 0 for quiz 0.
  """
  return quizn - 1 if quizn >= 2 else quizn