def get_days(offered):
    """Gets the days a course is offered
    @params
        'offered': String representing the days a course is offered
        Example: 'MWF' -> Monday, Wednesday, Friday
    Returns
        Set of abbreviated days the course is offered
    """
    days = ['Th', 'M', 'T', 'W', 'F', 'S']
    result = set()
    for day in days:
        if day in offered:
            result.add(day)
            offered = offered.replace(day, '', 1)
    return result