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