#include <cstdlib>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <omp.h>
#include <vector>

int main(int argc, char* argv[])
{
	int thread_count = omp_get_max_threads();
	if ( argc >= 2 )
		thread_count = atoi(argv[1]);

	std::vector<double> values;
	std::copy(std::istream_iterator<double>(std::cin),
		std::istream_iterator<double>(),
		std::back_inserter(values));

	double sum = 0;

	#pragma omp parallel for num_threads(thread_count) schedule(static) \
		default(none) shared(values) reduction(+:sum)
	for ( size_t index = 0; index < values.size(); ++index )
		sum += values[index];

	std::cout << sum / values.size() << std::endl;
	return 0;
}