class Student(Person):
    #   Class Constructor
        def __init__(self, firstName, lastName, idNum, scores):
            self.firstName = firstName
            self.lastName = lastName
            self.idNumber = idNum
            self.scores = scores
    #
        def calculate(self):
            avg = sum(self.scores) / len(self.scores)
            if ((90<=avg) and (avg<=100)):
                return str("O")
            elif ((80<=avg) and (avg<90)):
                return str("E")
            elif ((70<=avg) and (avg<80)):
                return str("A")
            elif ((55<=avg) and (avg<70)):
                return str("P")
            elif ((40<=avg) and (avg<55)):
                return str("D")
            else:
                return str("T")