#include <iostream>
#include <vector>
#include <deque>
#include <stack>
#include <memory>
#include <functional>
#include <algorithm>
#include <map>
#include <list>
#include <complex>
#include <string>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <numeric>
#include <array>
using namespace std;
typedef std::pair<int, int> pii;
typedef long long int ll;

#define pb push_back

const long long int MOD = 1e9+7;

int main(){
		
	int A, B, X, Y;

	cin >> A >> B >> X >> Y;

	double a = X * (double)B/A;
	double b = Y * (double)A/B;

	if(b <= X){
	 	printf("%.12f\n", b + Y);
	 	return 0;
	}
	
	if(a <= Y) printf("%.12f\n", a + X);

	return 0;
}