Calculation: 200-198+196-194+192-190+...+4-2=how much.
计算：200-198+196-194+192-190+…+4-2=多少．
<gadget id="calculator">4 - 4 - 200 - 198</gadget>
<output>-398</output>

<gadget id="calculator">100 / (-398)</gadget>
<output>-50/199 = around -0.251256</output>

<gadget id="calculator">(-398) * (-50/199)</gadget>
<output>100</output>

<result>100</result>