#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c,d;
	cin>>a>>b>>c>>d;
	if(a>=90&&b>=90&&c>=90&&d>=90){
		cout<<"A";
	}else if(a<90&&b>=90&&c>=90&&d>=90||a>=90&&b<90&&c>=90&&d>=90||a>=90&&b>=90&&c<90&&d>=90||a<90&&b>=90&&c<90&&d>=90||a<90&&b>=90&&c>=90&&d<90||a>=90&&b<90&&c<90&&d>=90||a>=90&&b<90&&c>=90&&d<90||a>=90&&b>=90&&c<90&&d<90){
		cout<<"B";
	}else if(a>=90&&b<90&&c<90&&d<90||a<90&&b>=90&&c<90&&d<90||a<90&&b<90&&c>=90&&d<90||a<90&&b<90&&c<90&&d>=90){
		cout<<"C";
	}else if(a<90&&b<90&&c<90&&d<90){
		cout<<"D";
	}
}
/**************************************************************
	Problem: 1735
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/