#include <iostream>
#include <iomanip>
#include <sstream>
#include <string>

int main()
{
    std::cout << std::fixed << std::setprecision(2);
    std::string line;
    std::getline(std::cin, line);
    std::istringstream input(line);
    double sum = 0;
    int num = 0;
    double n;
    while(input >> n) {
        sum += n;
        ++num;
    }
    double avg = sum/num;
    std::cout << avg << '\n';
}