def calculate_grade(marks):
    if marks >= 90:
        return 'A'
    elif marks >= 80:
        return 'B'
    elif marks >= 70:
        return 'C'
    elif marks >= 60:
        return 'D'
    else:
        return 'F'


m = int(input("Enter your marks: \n"))
print("Your grade is", calculate_grade(m))