#include <bits/stdc++.h>
using namespace std;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);  
	double a, b, x, y;
	cin >> a >> b >> x >> y;
	double s, t;
	s = x * b / a;
	t = y * a / b;
	double ans = y >= s ? s + x : t + y;
	cout << setprecision(20) << ans << endl;
	return 0;	
}