#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: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/