#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    double mark,sum=0;
    for(int i=0;i<4;i++){
        if(!(cin>>mark)||mark<0||mark>100){
            cout<<"Invalid input"<<endl;
            return 0;
        }
        sum +=mark;
    }
    sum+=mark;
}
cout<<fixed<<setprecision(2)<<sum/4.0<<endl;
return 0;
}