import math


def calc_n_sheets(n_pages: int) -> int:
    """
    How many sheets does this number of pages need, on the basis of 2 pages
    per sheet?
    """
    # NB PyCharm's type checker seems to think math.ceil() returns a float,
    # but it returns an int.
    # noinspection PyTypeChecker
    return math.ceil(n_pages / 2)