class CharacterReader {

    String consumeLetterThenDigitSequence() {
        int start = pos;
        while (pos < length) {
            char c = input[pos];
            if ((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'))
                pos++;
            else
                break;
        }
        while (!isEmpty()) {
            char c = input[pos];
            if (c >= '0' && c <= '9')
                pos++;
            else
                break;
        }

        return new String(input, start, pos - start);
    }

      CharacterReader(String input);

}