Calculation: 2001**2-2000**2+1999**2-1998**2+...-3+3**2-2**2+1=how much.
计算：2001**2-2000**2+1999**2-1998**2+…-3+3**2-2**2+1=多少．
<gadget id="calculator">2_001 + 1</gadget>
<output>2_002</output>

<gadget id="calculator">2_001 / 2</gadget>
<output>2_001/2 = around 1_000.5</output>

<gadget id="calculator">2_002 * (2_001/2)</gadget>
<output>2_003_001</output>

<result>2_003_001</result>