#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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