public static String getCategories() {
        int round = Server_Loader.round;
        Config config = Server_Loader.questions_data;
        int i = 1;
        StringBuilder sb = new StringBuilder();
        while(config.isSet("Category#" + round + "#" + i)) {
            if(!sb.toString().equals("")) sb.append(" ");
            sb.append(config.getString("Category#" + round + "#" + i));
            i++;
        }
        if(sb.toString().equals("")) warn("Can't get categories (contest " + Server_Loader.contestName + ", round " + Server_Loader.round + ")", true);
        return sb.toString();
    }