//% examen-ete-2003
#include<iostream.h>

double moyenne;
double moyenne_mat(double mat1, double mat2, double mat3){
	moyenne = (mat1 + mat2 + mat3)/3.;
	return moyenne;
}

class matiere {
public:
 int code;
 double mat1, mat2, mat3, moyenne;
 matiere (){
 mat1 =0;
 mat2 =0;
 mat3 =0;
 moyenne = 0;
 } 
};
int main(){
	matiere etud;
	int code;
	double m1, m2, m3;
	
 cin >> code >> etud.mat1 >> etud.mat2 >> etud.mat3;
 	m1 = etud.mat1;
	m2 = etud.mat2;
	m3 = etud.mat3;
 cout << moyenne_mat(m1, m2, m3) << endl;
 }