#include <stdio.h>

int main() {
    int n;
    while (scanf("%d", &n) != EOF) {
        if (90 <= n && n <= 100) {
            printf("A");
        } else if (80 <= n && n <= 89) {
            printf("B");
        }

        else if (70 <= n && n <= 79) {
            printf("C");
        } else if (60 <= n && n <= 69) {
            printf("D");
        } else if (0 <= n && n <= 59) {
            printf("E");
        } else {
            printf("F");
        }
    }

    return 0;
}