#include <iostream>
#include <sstream>
#include <math.h>
#include <stack>
#include <set>
#include <algorithm>
#include <string>
#include <queue>
#include <stack>
#include <map>
#include <cstdio>
#include <vector>
#include <iomanip>
using namespace std;

#define INF (1 << 30)
#define INFLL (1LL << 60)

int main() {
	double a,b,x,y;
	cin >> a >> b >> x >> y;
	cout << fixed << setprecision(7);
	if(b*x/a < y){
		cout << b*x/a + x << endl;
	}else{
		cout << a*y/b + y << endl;
	}
	return 0;
}