#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    int m,e,s,h;
    cin>>m>>E>>s>>h;
    if(m<0||m>100||e<0||e>100||s<0||s>100||h<0||h>100){
        cout<<"Invalid input";
        return 0;
    }
    double average=(m+e+s+h)/4.0;
    cout<<fixed<<setprecision(2)<<average;
    return 0;
}