private function inputAccruedNationalNumber()
    {
        $lengthOfNationalNumber = mb_strlen($this->nationalNumber);
        if ($lengthOfNationalNumber > 0) {
            $tempNationalNumber = '';
            for ($i = 0; $i < $lengthOfNationalNumber; $i++) {
                $tempNationalNumber = $this->inputDigitHelper(mb_substr($this->nationalNumber, $i, 1));
            }
            return $this->ableToFormat ? $this->appendNationalNumber($tempNationalNumber) : $this->accruedInput;
        }

        return $this->prefixBeforeNationalNumber;
    }