#include <iostream>
using namespace std;
class Marks{
    protected:
    int math,science,english;
    public:
    void display(){
        cin>>math>>science>>english;
        if(math<0 || math>100 || science<0 || science>100 || english<0 || english>100){
            cout<<"Invalid input";
        }
    }
};
class Activities{
    protected:
    int act;
    public:
    void display1(){
        cin>>act;
        if(act<0 || act>100){
            cout<<"Invalid input";
        }
    }
};
class Result : public Marks,public Activities {
    protected:
    int re=math+science+english+act;
    public:
    void disp(){
        cin>>re;
        if(re>=250){
             cout<<re<<"A";
        }
        else if(re>=200 && re<250){
             cout<<re<<"B";
        }
        else if(re<200 && re>=150){
             cout<<re<<"C";
        }
        else{
             cout<<"F";
        }
};
int main() {
    Result r;
    r.display();
    r.display1();
    r.disp();
    return 0;
}