Uncle Wang is going to make a 20-section iron chimney with a length and width of 4 decimeters and a height of 1 meter. How much iron will he need at least? (neglected at joints)
王叔叔要做20节长和宽都是4分米、高1米的铁皮烟囱，至少需要多少铁皮？(接头处忽略不计)
<gadget id="calculator">4 * 1 * 10</gadget>
<output>40</output>

<gadget id="calculator">40 + 40</gadget>
<output>80</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">80 * 2 * (1/5)</gadget>
<output>32</output>

<result>32</result>