def polygonal_number(sides: int, n: int) -> int:
    """
    Returns the n-th polygonal number for a given number of sides.
    A polygonal number is a number represented as dots or pebbles arranged in the shape of a regular polygon.

    :param sides: The number of sides of the polygon
    :param n: A positive number
    :return: The n-th polygonal number for a given number of sides
    """
    return (sides - 2)*n*(n-1)//2 + n