#include "stdio.h"
main()
{
   float num;
   char grade;
   scanf("%d",&num);
   if(num>=90) grade='A';
   else if (num>=80&&num<90) grade='B';
   else if (num>=70&&num<80) grade='C';
   else if (num>=60&&num<70) grade='D';
   else grade='E';
   printf("%c",grade);
}