200*199-199*198+198*197-197*196+...+2*1=how much.
200*199-199*198+198*197-197*196+…+2*1=多少．
<gadget id="calculator">199 + 1</gadget>
<output>200</output>

<gadget id="calculator">200 / 2</gadget>
<output>100</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">200 * 100 * (1/2) * 1</gadget>
<output>10_000</output>

<gadget id="calculator">2 * 1 * 10_000</gadget>
<output>20_000</output>

<result>20_000</result>