There are a bunch of chess pieces, 3 pieces with 3 land numbers, and 2 pieces left at the end; 5 pieces with 5 land numbers, and 3 pieces left at the end; 7 pieces with 7 land numbers, and 2 pieces left at the end. How many pieces are there at least in this pile.
有一堆棋子，3个3个地数，最后余下2个；5个5个地数，最后余下3个；7个7个地数，最后余下2个．这堆棋子最少有多少个．
<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<gadget id="calculator">21 + 2</gadget>
<output>23</output>

<result>23</result>