#include <iostream>
#include <string>
#include <fstream>
#include <iomanip>
int main()
{
	int a, b, x, y;
	std::cin >> a;
	std::cin >> b;
	std::cin >> x;
	std::cin >> y;

	double max_wa = a > b ? a : b, min_wa = a > b ? b : a;
	double max_eki = x > y ? x : y, min_eki = x > y ? y : x;
	
	if(max_eki * min_wa / max_wa > min_eki)
	{
		std::cout << min_eki + min_eki * max_wa / min_wa << std::endl;
	}
	else
	{
		std::cout << std::setprecision(12) << max_eki + max_eki * min_wa / max_wa << std::endl;
	}
	
}