#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<<aetprecision(2)<<average<<endl;
}
return 0;
}