# include<iostream> using namespace std; int main(){ int c; cin>>c; if(c>=90){ cout<<"A"<<endl; } else if(c>=80&&c<90){ cout<<"B"<<endl; } else if(c>=70&&c<80){ cout<<"C"<<endl; } else if(c>=60&&c<70){ cout<<"D"<<endl; } else{ cout<<"不及格"<<endl; } return 0; }