1-2+3-4...+2011-2012+2013=how much.
1-2+3-4…+2011-2012+2013=多少．
<gadget id="calculator">2_011 - 2_012</gadget>
<output>-1</output>

<gadget id="calculator">(-1) + 2_013</gadget>
<output>2_012</output>

<gadget id="calculator">2_013 - 2_012</gadget>
<output>1</output>

<gadget id="calculator">1 + 1_006</gadget>
<output>1_007</output>

<result>1_007</result>