What is the calculation result of the formula 2011-2009+2007-2005+…-…+3-1?
算式2011-2009+2007-2005+…-…+3-1的计算结果是多少．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 * 503</gadget>
<output>1_006</output>

<result>1_006</result>