#206. Letter grade
You get a score. Print A for 90 or more, B for 80-89, C for 70-79, D for 60-69, and F otherwise.
### Input
One integer (0 ≤ score ≤ 100).
### Output
One letter.
Examples
Input
16
Output
F
Input
54
Output
F
💡 You can solve it with Python, JavaScript or blocks. Read the input line by line with input(). Don't print a question (like input("Number: ")). Print exactly what the output asks for, nothing more.