Regulations: x★y=(x+y)+(xy), find 13★5; 13★(5★4).
规定：x★y=(x+y)+(x-y)，求13★5；13★(5★4)．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<gadget id="calculator">13 + 10</gadget>
<output>23</output>

<gadget id="calculator">13 - 10</gadget>
<output>3</output>

<gadget id="calculator">23 + 3</gadget>
<output>26</output>

<result>26</result>