#include <stdio.h>

int main() {
	int x;
	scanf("%d",&x);
	if (   x>=90    )
		printf("S \n");
	else if (  x>=80     )
		printf("A \n");
	else if (  x>=60   )
		printf(" B \n");
	else
		printf(" D\n");
	return 0;
}