#include <stdio.h>

int main(void) {
	// your code goes here
    int score;
    printf("input score:");
    scanf("%d",&score);
    if(score>=0)
    {
    if(score>100) printf("error");
    else if(score>=90) printf("A");
    else if(score>=80) printf("B");
    else if(score>=70) printf("C");
    else if(score>=60) printf("D");
    else printf("E");}
    else printf("error");
	return 0;
}