#173 medie1

#include <iostream>
#include <iomanip>
using namespace std;

int main(void)
{
int x,y,z;
float m;
cin>>x>>y>>z;
m=(x+y+z)/3.;
m=(int)(m*100)/100.;
cout<<fixed<<setprecision(2)<<m;

    return 0;
}