Calculation: 1-2-3+4+5-6-7+8+9-...+2004+2005-2006-2007+4017=how much.
计算：1-2-3+4+5-6-7+8+9-…+2004+2005-2006-2007+4017=多少．
<gadget id="calculator">2_004 / 4</gadget>
<output>501</output>

<gadget id="calculator">501 * 4</gadget>
<output>2_004</output>

<gadget id="calculator">2_004 - 2_006 - 2_007</gadget>
<output>-2_009</output>

<gadget id="calculator">1 + (-2_009) + 4_017</gadget>
<output>2_009</output>

<result>2_009</result>