Use some square pieces of paper with a side length of 1 decimeter, and place them one by one in order. It is required that the vertex of the back-swing paper must coincide with the center of the previous one. When n=20, the shape of the assembled figure How many decimeters is the circumference?
用一些边长1分米的正方形纸片，按顺序一张一张摆下去，要求后摆的纸片必须有一个顶点与前一张的中心重合，当n=20时，所拼成图形的周长是都多少分米？
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">20 - 2</gadget>
<output>18</output>

<gadget id="calculator">2 * 18</gadget>
<output>36</output>

<gadget id="calculator">6 + 36</gadget>
<output>42</output>

<result>42</result>