#include <stdio.h>

int main() {
    int score;

    scanf("%d", &score);

    if (score >= 90) {
        printf("A\n");
    } else if (score >= 80) {
        printf("B\n");
    } else if (score >= 70) {
        printf("C\n");
    } else if (score >= 60) {
        printf("D\n");
    } else {
        printf("0000\n");
    }
    return 0;
}
/**************************************************************
	Problem: 1035
	User: fuhoubin
	Language: C++
	Result: Wrong Answer
****************************************************************/