// Page 126 - 127

import java.util.Scanner;
public class Prog_10_4
{
	public static void main(String[] args)
	{
		Scanner input=new Scanner(System.in);
		double score=0.0;
		String grade;
		score=input.nextDouble();
		grade=convertToGrade(score);
		System.out.println("the grade is: " + grade);
	}
	private static String convertToGrade(double score)
	{
	      if( score >= 89.5 )
	           return "A";
	      else if ( score >= 79.5 )
	           return "B";
	      else if ( score >= 69.5 )
	           return "C";
	      else if ( score >= 59.5 )
	           return "D";
	      else
	           return "F";
	}
}