There are 20 two-headed monsters and three-headed monsters in the mysterious kingdom, with a total of 43 heads. Well, do you know how many three-headed monsters there are?
神秘王国有两头怪和三头怪共20只，一共有43个头．那么么你知道有多少个三头怪．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">43 - 40</gadget>
<output>3</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<result>3</result>