public int total() {
        int result = 0;
        String separator = "";
        for (Object operando : operators) {
            if (operando != null) {
                System.out.print(separator + operando.toString());
                if (operando.getClass().getSimpleName().equals("Summation")) {
                    result += ((Summation) operando).sum();
                } else {
                    result += ((Subtraction) operando).subtract();
                }
            }
            separator = "+";
        }
        System.out.print(">>> ");
        return result;
    }