import java.util.*;

public class Run {
    public static void main (String arg[]) {
        Scanner scan = new Scanner(System.in);
        double ans = 0;

        int A = scan.nextInt();
        int B = scan.nextInt();
        int X = scan.nextInt();
        int Y = scan.nextInt();

        double r = ((double) B)/A;
        double x = ((double) X);
        double y = X * r;

        if (Y < y) {
            y = Y;
            x = Y * (1/r);
        }

        ans = x + y;

       System.out.println(ans);
    }
}