//
//
//	Q3
//	Name:	Scores.java
//	..
//	Goal:	Read a score (0-5), out letter grade
//
//

import java.util.Scanner;

public class Scores
{
	public static void main(String[] args)
	{
		Scanner kb = new Scanner(System.in);
		int score;

		System.out.print("Input a score: ");
		score = kb.nextInt();

		switch(score)
		{
			case 5:
				System.out.println("A");
				break;
			case 4:
				System.out.println("B");
				break;
			case 3:
				System.out.println("C");
				break;
			case 2:
				System.out.println("D");
				break;
			case 0:
				System.out.println("F");
				break;
		}

	}
}