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

using namespace std;

int main(int argc, const char* argv[])
{
	double A, B, X, Y;
	cin >> A >> B >> X >> Y;
	cout << fixed << setprecision(6);
	if (X / A > Y / B) {
		cout << Y / B * (A + B) << endl;
	}
	else {
		cout << X / A * (A + B) << endl;
	}
	return 0;
}