I am new to python coding and i do not understand how to use a variable from another method

Here is what i have tried: I do not understand how can i use a variable from another method of same class. Also please explain how can i use a variable from a method in different class. I tried searching but could not find a solution. So what i did to pass the test cases is to copy code from calculate_percentage and paste it in find_grade method. It worked but i think this is the worst method. So please tell a possible solution. Thanks

#!/bin/python3

#Enter your code here. Read input from STDIN. Print output to STDOUT
class Student:
    def __init__(self,roll,name,marks_list):
        self.roll=roll
        self.name=name
        self.marks_list=marks_list 
    def calculate_percentage(self):
        length=len(self.marks_list)
        sum=0
        for i in self.marks_list:
            sum+=i 
        percent=sum/length 
        return int(percent)
    def find_grade(self,percent):
        if percent>=80:
            return 'A'
        elif percent>=60 and percent<80:
            return 'B'
        elif percent>=40 and percent<60:
            return 'C'
        elif percent<40:
            return 'F'

if __name__ == '__main__':
    roll=int(input())
    name=input()
    count=int(input())
    marks=[]
    for i in range(count):
        marks.append(int(input()))
    s=Student(roll,name,marks)
    print(s.calculate_percentage())
    print(s.find_grade())

i am getting the error:

print(s.find_grade())
TypeError: find_grade() missing 1 required positional argument: 'percent'