#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c,d,s=0;
	cin>>a>>b>>c>>d;
	if(a>=90) s=s+1;
	if(b>=90) s=s+1;
	if(c>=90) s=s+1;
	if(d>=90) s=s+1;
	if(s==4) cout<<"A";
	else if(s>=2) cout<<"B";
	else if(s==1) cout<<"C";
	else cout<<"D";
    return 0;
}

/**************************************************************
	Problem: 1735
	User: admin
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/