#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: wangyiyang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/