# Problem 6. Student grades

mark = int(input("Enter your marks: "))

if(mark >= 90):
    print("Your grade is O")
elif (mark >= 80):
    print("Your grade is A")
elif (mark >= 70):
    print("Your grade is B")
elif (mark >= 60):
    print("Your grade is C")
elif (mark >= 50):
    print("Your grade is D")
else :
    print("Your grade is F")
    
    