import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int x = sc.nextInt();
        int y = sc.nextInt();
        double ans;
        if (x * b <= y * a) {
            ans = (double)x / a * b + x;
        } else {
            ans = (double)y / b * a + y;
        }
        System.out.println(ans);
    }
}