#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(50<=n<80){
		cout<<"E";
	}else{
		if(40<=n<50){
			cout<<"D";
		}else{
			if(20<=n<40){
				cout<<"C";
			}else{
				if(10<=n<20){
					cout<<"B";
				}else{
					if(n<10){
						cout<<"A";
					}
				}
			}
		}
	}
	
	return 0;
}
/**************************************************************
	Problem: 1044
	User: linyuhang
	Language: C++
	Result: Wrong Answer
****************************************************************/