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