#include<stdio.h>
int main()
{
int score,grade;
scanf("%d",&score);
grade=score/10;
switch (grade)
{
case 10:
case 9:
printf("A
");
break;
case 8:
printf("B
");
break;
case 7:printf("C
");
break;
case 6:printf("D
");
break;
case 5:
case 4:
case 3:
case 2:
case 1:
case 0:printf("F
");
break;
default:
// printf("什么鬼
");
break;
}
return 0;
}
//注意：在两个数做运算时，只要有一个是浮点数，计算的结果均为浮点数！