99. A pile of chess pieces, each time take away half, then put back one, after 4 times there are still 3 pieces left, originally there were $\qquad$ pieces.

将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。 

Note: The last sentence is a note and not part of the translation. The actual translation is above.
Answer: 18