#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int math,english,science,history;
    
    if(!(cin>>math>>english>>science>>history)){
        return 0;
    }
    if (math<0 ||math>100||english<0 ||english>100||science<0 ||science>100||history<0 ||history>100||){
        cout<<"Invalid Input"<<endl;
    }else{
        float average=(math+english+science+history)/4.0;
        cout<<fixed<<setprecision(2)<<average<<endl;
    }
    return 0;
}