import java.util.Scanner;

public class Test {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		double a, b, ra, rb, ca, cb, ans;
		ra = sc.nextDouble();
		rb = sc.nextDouble();
		a = sc.nextDouble();
		b = sc.nextDouble();
		ca = b*ra/rb;
		cb = a*rb/ra;
		if(a > ca){
			System.out.println(ca+b);
		} else if(b > cb){
			System.out.println(a+cb);
		} else {
			System.out.println(a+b);
		}
	}
}