#include<bits/stdc++.h> using namespace std; int main() { int a; cin>>a; if(a >=90 && a<=100){ cout<<"A"<<endl; }else if(a >= 80 && a <90){ cout<<"B"<<endl; }else if(a >= 70 && a< 80){ cout<<"C"<<endl; }else if(a >= 60 && a< 70){ cout<<"D"<<endl; }else{ cout<<"不及格"<<endl; } return 0; }