#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    double marks[4];
    float sum;
    for(int i=0;i<4;i++){
        cin>>marks[i];
        if>>marks[i]<0||marks[i]>100
{
    cout<<"Invalid input";
    return 0;
}  
else {
    sum+=[i];
}
        
    }
    sum=sum/4;
    cout<<fioxed<<setprecision(2)<<sum;
}