#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;
}