#include<bits/stdc++.h> using namespace std; int main() { int a; cin >> a; if (a >= 90) { cout << "A" << endl; } else if (a >= 80) { cout << "B" << endl; } else if (a >= 70) { cout << "C" << endl; } else if (a >= 60) { cout << "D" << endl; } else { cout << "F" << endl; } return 0; }