import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
		
        Scanner sc = new Scanner(System.in);
		
       	double A = sc.nextInt();
        double B = sc.nextInt();
		double X = sc.nextInt();
        double Y = sc.nextInt();
		
		double max=0;
		
		if(A*Y<=B*X){
			max=Y*(A+B)/B;
		}else if(A*Y>B*X){
			max=X*(A+B)/A;
		}
		
        System.out.println(max);
    }
}