// PR Bab 03, soal 2 -- pembahasan.

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

int main() {
    int a, b, c;
    cin >> a >> b >> c;

    double rata = (a + b + c) / 3.0;   // 3.0, bukan 3
    cout << fixed << setprecision(2) << rata << "\n";
    return 0;
}