#include <iostream>
#include <iterator>
#include <algorithm>
#include <numeric>
#include <functional>
#include <vector>
 
int main() {
   std::vector<int> vector((std::istream_iterator<int>(std::cin)), std::istream_iterator<int>());
   std::vector<int>::iterator it = std::find_if(
         vector.begin(),
         vector.end(),
         std::bind2nd(std::less<int>(), 0));
   std::cout << static_cast<double>(std::accumulate(vector.begin(), it, 0))
         / std::distance(vector.begin(), it) << std::endl;
}

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