#include <iostream>
#include <string>
#include <vector>
#include <map>

using namespace std;

int main(void) {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);
	std::cout << std::fixed;
	double A, B, X, Y;
	double result;
	cin >> A >> B >> X >> Y;
	double s = X * B / A;
	double t = Y * A / B;
	if (s < Y) {
		result = X + s;
	} else {
		result = Y + t;
	}
	//cout.precision(10);
	cout << result << endl;
}