#include <bits/stdc++.h>

using namespace std;

int main() {
    int score;
    cin >> score;

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