#include <stdio.h>

int main(void) {
	int x;

	scanf("%d", &x);

	switch (x / 10) {
		case 10:
		case 9:
			printf("A+");
			break;
		case 8:
			printf("A");
			break;
		case 7:
			printf("B");
			break;
		case 6:
			printf("C");
			break;
		default:
			printf("F");
	}
	printf("\n");

	return 0;
}