#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    if (50<=n && n<80){
        cout<<"E"<<endl;
    }
    else if (40<=n && n<50){
        cout<<"D"<<endl;
    }
    else if (20<=n && n<40){
        cout<<"C"<<endl;
    }
    else if (10<=n && n<20){
        cout<<"B"<<endl;
    }
    else if (n<10){
        cout<<"A"<<endl;
    }
    return 0;
}
/**************************************************************
	Problem: 1044
	User: HUANGYIBO
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/