It is stipulated that A☆B=A*B-(A+B), then how much is 5☆4, and how much is (3☆4)☆5?
规定A☆B=A*B-(A+B)，那么5☆4是多少，(3☆4)☆5是多少？
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">20 - 9</gadget>
<output>11</output>

<result>11</result>