public int accept(int ins_num, int income_seq, String content) throws RemoteException {
    if (!work) return -1;

    Instance res = instances.get(ins_num);

    if (res == null) return -1;
    else {

      if (income_seq >= res.n_p) {

        res.n_p = income_seq;

        res.n_a = income_seq;

        res.content = content;

        res.decided = true;

        INS_NUM++;

        return income_seq;
      }
    }

    return -1;
  }
  public Instance prepare(int ins_num, int income_seq) throws RemoteException {
    if (!work) return null;

    Instance res = instances.get(ins_num);

    if (res == null) return null;
    else {

      if (income_seq > res.n_p) {

        res.n_p = income_seq;

        return res;
      } else return null;
    }
  }