下面程序结果为：(     )

class Top {
    static int x = 1;
    public Top(int y) {
        x *= 3;
    }
}
class Middle extends Top {
    public Middle() {
        x += 1;
    }
    public static void main(String[] args) {
        Middle m = new Middle();
        System.out.println(x);
    }
}