#include<bits/stdc++.h>
using namespace std;
const double a=10000000,b=1000000;
long double p1,p0,f,l,n,ans;
int main()
{
	cin>>p1>>p0>>f>>l;
	n=p1+p0+f+l;
	if(n==1) 
	{
		if(p1==1) cout<<"EX+";
		else if(p0==1) cout<<"EX+";
		else cout<<"D";
		return 0;
	}
	ans=(p1*(a/n+1))+(p0*(a/n))+(f*(a/n));
	if(ans>9.9*b) cout<<"EX+";
	else if(ans>=9.8*b) cout<<"EX+";
	else if(ans>=9.5*b) cout<<"AA";
	else if(ans>=9.2*b) cout<<"A";
	else if(ans>=8.9*b) cout<<"B";
	else if(ans>=8.6*b) cout<<"C";
	else cout<<"D";
	//cout<<ans;
	return 0;
}

求在原来上面改