include

using namespace std;

int main() {

int score;
cin >> score;
if (score >= 0) {
	cout << "A";
} else if ( score >= 80 && score < 90) {
	cout << "B";
} else if ( score >= 70 && score < 80) {
	cout << "C";
} else if ( score >= 60 && score < 70) {
	cout << "D";
} else {
}
return 0;

}