#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<ctime>
#include<complex>
#include<functional>
#include<climits>
#include<cassert>
#include<iterator>
using namespace std;
double a, b, x, y;
int main(){
	cin >> a >> b >> x >> y;
	double ans = x;
	ans *= b;
	ans /= a;
	double out = 0.0;
	if (ans <=y){
		out = x + ans;
	}
	ans = y;
	ans *= a;
	ans /= b;
	if (ans <= x){
		out = max(out, y + ans);
	}
	printf("%.16f\n", out);
	return 0;
}