#include<bits/stdc++.h>
using namespace std;
int main()
{
int a;
cin>>a;
if(a>=50&&a<=80){
	cout<<"E";
}
else if(a>=40&&a<50){
	cout<<"D";
}
else if(a>=20&&a<40){
	cout<<"C";
}
	else if(a>=10&&a<20){
	cout<<"B";
	
}else{
	cout<<"A";
}



	return 0;
}

/**************************************************************
	Problem: 1044
	User: hbq
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/