#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>

using namespace std;

int main(){
	int i, j;
	double a, b, x, y;

	cin >> a >> b >> x >> y;


	if (a > b) {
		while (true)
		{
			double num = x * (b / a);
			if (num <= y) {
				y = num;
				break;
			}
			else {
				x -= 0.000001;
			}
		}
	}
	else {

		while (true)
		{
			double num = y * (a / b);
			if (num <= x) {
				x = num;
				break;
			}
			else {
				y -= 0.000001;
			}
		}
		

	}
	


	cout << fixed <<setprecision(8)<< y + x << endl;






	getchar();
	getchar();
	return 0;
}