#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; }