(1+2+3+...+2008+2009+2008+...+3+2+1)/2009=how much.
(1+2+3+…+2008+2009+2008+…+3+2+1)/2009=多少．
<gadget id="calculator">1 + 2_008</gadget>
<output>2_009</output>

<gadget id="calculator">2_008 / 2</gadget>
<output>1_004</output>

<gadget id="calculator">2_009 * 1_004 * 2</gadget>
<output>4_034_072</output>

<gadget id="calculator">4_034_072 + 2_009</gadget>
<output>4_036_081</output>

<gadget id="calculator">4_036_081 / 2_009</gadget>
<output>2_009</output>

<result>2_009</result>