Calculation: 1000+999-998-997+996+995-994-993+...+904+903-902-901.
计算：1000+999-998-997+996+995-994-993+…+904+903-902-901．
<gadget id="calculator">903 - 902 - 901</gadget>
<output>-900</output>

<gadget id="calculator">904 + (-900)</gadget>
<output>4</output>

<gadget id="calculator">4 * 25</gadget>
<output>100</output>

<result>100</result>