#include <vector>
#include <algorithm>
#include <stdexcept>

double median(std::vector<double> vec)
{
	std::vector<double>::size_type mid, size;

	size = vec.size();

	if (size == 0)
		throw std::domain_error("median of an empty vector");

	sort(vec.begin(), vec.end());

	mid = size / 2;

	return size % 2 == 0 ? (vec[mid] + vec[mid - 1]) / 2
			     : vec[mid];

}