#include <stdio.h>
int main()
{
int score = 0;
scanf("%d", &score);
int c = score / 10;
if (score >= 0)
{
switch (c)
{
case 9:
case 10:
printf("A\n");
break;
case 8:
printf("B\n");
break;
case 7:
printf("C\n");
break;
case 6:
printf("D\n");
break;
case 5:
case 4:
case 3:
case 2:
case 1:
case 0:
printf("E\n");
break;
default:
printf("F\n");
break;
}
}
else
{
printf("F\n");
}
return 0;
} 
京公网安备 11010502036488号