#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';
}
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