class Student:

 def __init__(self, name, marks):
   self.name = name
   self.marks = marks
   self.grade = ""

 def calculateGrade(self):
   if self.marks < 40:
     self.grade = "D"
   elif self.marks < 60:
     self.grade = "C"
   elif self.marks < 80:
     self.grade = "B"
   else: 
     self.grade = "A"

  def displayGrade(self):
   print(self.grade)

st1 = Student("St1", 10)
st2 = Student("St2", 45)

st1.calculateGrade()
st1.displayGrade()

st2.calculateGrade()
st2.displayGrade()