#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<<"不及格"<<endl; } return 0; }