Calculation: -1+3-5+7-9+11-...+2007-2009+2011-2013+2015.
计算：-1+3-5+7-9+11-…+2007-2009+2011-2013+2015．
<gadget id="calculator">2_015 + 1</gadget>
<output>2_016</output>

<gadget id="calculator">2_016 / 2 / 2</gadget>
<output>504</output>

<gadget id="calculator">504 * 2</gadget>
<output>1_008</output>

<result>1_008</result>