#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c,d,h=0;
	cin>>a>>b>>c>>d;
	if(a>=90) h++;
	if(b>=90) h++;
	if(c>=90) h++;
	if(d>=90) h++;
	if(h==4) cout<<"A";
	if(h==3||h==2) cout<<"B";
	if(h==1) cout<<"C";
	if(h==0) cout<<"D";
}
/**************************************************************
	Problem: 1735
	User: linzihang
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/