@Override
    public String toString() {
        String s = "{ ";
        int aux = 0;
        for (int i = 0; i < listas.length; i++) {
            for (int j = 0; j < listas[i].size(); j++) {
                s += listas[i].get(j).toString() + ", ";
                if (++aux == 5) {
                    s += "\n";
                }
            }
        }
        return s + "}";
    }