import doctest

from typing import Callable


# term :: int -> int
def cube(x: int) -> int:
    """
    Evaluates cube of given number.
    >>> cube(3)
    27
    >>> cube(5)
    125
    """
    return x * x * x


# term :: int -> int
def summation(
    n: int,
    term: Callable[[int], int],
) -> int:
    """
    Sums first n numbers of series.
    >>> summation(5, cube)
    225
    >>> summation(5, lambda k: 8 // ((4 * k - 3) * (4 * k - 1)))
    2
    """
    total = 0
    for k in range(1, n + 1):
        total += term(k)
    return total


if __name__ == "__main__":
    doctest.testmod()