def age_category(age, average=-1):
    """
    We divided the age into 5 steps taking care of the responsibility that a person has of himself
    and looking at how mush "strength" it has. This is an insteresting parameter to change while
    seeing inference.
    In case of nan values we put the average eta of the people who was embarked
    :param age: int with number
    :param average: average eta of people
    :return: class. -1 is returned in case of some strange value
    """
    if 'nan' in str(age):
        age = average
    if age < 11:
        return 0
    elif age < 20:
        return 1
    elif age < 40:
        return 2
    elif age < 60:
        return 3
    elif age < 200:
        return 4
    return -1