#include<bits/stdc++.h>
using namespace std;

int main(){
	int n;
	while(cin >> n){
		if(n >= 90)
			cout <<"A" <<endl;
		else if(n >= 80)
			cout << "B" <<endl;
		else if(n >= 70)
			cout << "C"<<endl;
		else if(n >= 60)
			cout << "D" <<endl;
		else
			cout << "E" <<endl;
	}				
	return 0;
}