int quickComputation();			// process the result "quick and dirty"
int accurateComputation();		// process the result "accurate but slow"

// outside declared because lifetime of accurateComputation() might exceed
// lifetime of bestResultInTime()
std::future<int> f;

int bestResultInTime()
{
	// define the time slot to get the answer
	auto tp = std::chrono::system_clock::now() + std::chrono::minutes(1);

	// start both a quick and an accurate computation
	f = std::async(std::launch::async, accurateComputation);
	int guess = quickComputation();

	// give accurate computation the rest of the time slot
	std::future_status s = f.wait_until(tp);

	// return the best computation result we have
	if (s == std::future_status::ready)
		return f.get();
	else
		return guess;	// accurateComputation() CONTINUES!!!!!
}