#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <set>
using namespace std;

int main(){
	int a,b,x,y;
	cin >> x >> y >> a >> b;

	double z = 1.0*a/x*y;
	if(b>=z){
		printf("%.12f\n", a+z);
	}else{
		z = 1.0*b/y*x;
		printf("%.12f\n", b+z);

	}
	return 0;
}