It is obvious that a five-layer figure is placed with chess pieces, the number of chess pieces in each two layers differs by 5, and 18 chess pieces are used in the innermost layer. How many chess pieces are used in total?
明明用棋子摆了一个五层图形，每两层棋子的个数相差5，最内层用了18个棋子，问一共用了多少个棋子？
<gadget id="calculator">18 * 5</gadget>
<output>90</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">5 + 10 + 15 + 20</gadget>
<output>50</output>

<gadget id="calculator">90 + 50</gadget>
<output>140</output>

<result>140</result>