def positive_sum3(a: int, b: int, c: int=0):
    """Normal exposed function

    Parameters
    ----------
    a: int
    b: int
    c: int, default 0
        All parameters are positive values.
        If negative, an exception is raised.

    Returns
    ----------
    int
    """
    if a<0 or b<0 or c<0:
        raise Exception('Error: Negative argument')
    return a+b+c