Calculation: 1-2+3-4+5-6+7-8+...-2010+2011-2012+2013.
计算：1-2+3-4+5-6+7-8+…-2010+2011-2012+2013．
<gadget id="calculator">2_011 - 2_012</gadget>
<output>-1</output>

<gadget id="calculator">(-2_010) + (-1) + 2_013</gadget>
<output>2</output>

<gadget id="calculator">2_012 / 2</gadget>
<output>1_006</output>

<gadget id="calculator">(-1) * 1_006</gadget>
<output>-1_006</output>

<gadget id="calculator">(-1_006) + 2_013</gadget>
<output>1_007</output>

<result>1_007</result>