1-2+3-4+5-6+...+2007-2008+2009.
1-2+3-4+5-6+…+2007-2008+2009．
<gadget id="calculator">1 + 2_009</gadget>
<output>2_010</output>

<gadget id="calculator">2_009 - 1</gadget>
<output>2_008</output>

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

<gadget id="calculator">1_004 + 1</gadget>
<output>1_005</output>

<gadget id="calculator">1_005 / 2</gadget>
<output>1_005/2 = around 502.5</output>

<gadget id="calculator">2_010 * (1_005/2)</gadget>
<output>1_010_025</output>

<gadget id="calculator">2_007 - 2_008</gadget>
<output>-1</output>

<gadget id="calculator">2 + (-1) + 2_009</gadget>
<output>2_010</output>

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

<gadget id="calculator">(-1) + 2_007</gadget>
<output>2_006</output>

<gadget id="calculator">2_006 / 2</gadget>
<output>1_003</output>

<gadget id="calculator">1_003 + 1</gadget>
<output>1_004</output>

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

<gadget id="calculator">2_010 * 502</gadget>
<output>1_009_020</output>

<gadget id="calculator">1_010_025 - 1_009_020</gadget>
<output>1_005</output>

<result>1_005</result>