#include <bits/stdc++.h>

using namespace std;

int main() {
    ios::sync_with_stdio(false); //读入输出优化的强迫症
    int a, b, c;
    cin >> a >> b >> c;
    int d = a + b + c;
    float e = d * 1.0 / 3;
    //设置输出为小数点后3位
    cout << fixed << setprecision(3);
    cout << e << endl;
    return 0;
}