import math


def all_possible_combinations_counter(subset_size,
                                      set_size):
    """
    Return a number (int) of all possible combinations of elements in size
    of a subset of a set.

    Parameters
    -------
    subset_size: int
        Size of the subset.
    set_size: int
        Size of the whole set.

    Returns
    -------
    int
        Number of all combinations.
    """
    f = math.factorial
    return f(set_size) / f(subset_size) / f(set_size - subset_size)