#include<iostream>
using namespace std;
int main(){
int a;
int b;
int c;
cin >> a;
cin >> b;
cin >> c;
printf("%.6f", float(a+b+c)/3);
}
#include<iostream>
using namespace std;
int main(){
int a;
int b;
int c;
cin >> a;
cin >> b;
cin >> c;
printf("%.6f", float(a+b+c)/3);
}