class Student(object):

    def __init__(self, name, score):

        self.name = name

        self.score = score

    def get_grade(self):

        try:

            if self.score not in list(range(101)):

                raise ValueError

            if self.score >= 80:

                return 'A'

            elif self.score >= 60:

                return 'B'

            return 'C'

        except:

            raise ValueError