1-3+5-7+9-11+...+2005-2007+2009=how much.
1-3+5-7+9-11+…+2005-2007+2009=多少．
<gadget id="calculator">1_004 / 2</gadget>
<output>502</output>

<gadget id="calculator">2 * 502</gadget>
<output>1_004</output>

<gadget id="calculator">2_009 - 1_004</gadget>
<output>1_005</output>

<result>1_005</result>