99-97+95-93+91-89+...+3-1=how much.
99-97+95-93+91-89+…+3-1=多少．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 * 25</gadget>
<output>50</output>

<result>50</result>