Calculation: 1-2+3-4+5-6+...-2006+2007.
计算：1-2+3-4+5-6+…-2006+2007．
<gadget id="calculator">(-2_006) + 2_007</gadget>
<output>1</output>

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

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

<gadget id="calculator">1 * 1_003</gadget>
<output>1_003</output>

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

<result>1_004</result>