def most_significant_bit(lst: np.ndarray) -> int:
    """
    A helper function that finds the position of the most significant bit in a 1darray of 1s and 0s,
    i.e. the first position where a 1 appears, reading left to right.

    :param lst: a 1d array of 0s and 1s with at least one 1
    :return: the first position in lst that a 1 appears
    """
    return np.argwhere(np.asarray(lst) == 1)[0][0]