#include<iostream>
#include<algorithm>
#include<iomanip>

int main() {
	double coffee_ratio, tea_ratio, total_coffee, total_tea;

	std::cin >> coffee_ratio >> tea_ratio >> total_coffee >> total_tea;
	

	double coffee = total_tea * coffee_ratio / tea_ratio;
	double tea = total_coffee * tea_ratio / coffee_ratio;

	double enoutea = 0.0;
	if (coffee > total_coffee) {
		enoutea = tea + tea * coffee / total_tea;
	} else if (tea > total_tea) {
		enoutea = coffee + coffee * tea / total_coffee;
	} else {
		enoutea = std::max(tea + tea * coffee / total_tea, coffee + coffee * tea / total_coffee);
	}

	std::cout << std::fixed << std::setprecision(6) << enoutea << std::endl;
}