"⊙" means a new operation, for any number a and b, there is a⊙b=a*b-(a+b). So what is the result of 5⊙4?
"⊙"表示一种新运算，对任何数a和b，有a⊙b=a*b-(a+b)．那么5⊙4的结果是多少．
<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>