It is known that Sn=1-2+3-4+5-6+...+(-1)n+n, where n is a positive integer. So how much is S2001+S2002=.
已知Sn=1-2+3-4+5-6+…+(-1)n+n，其中n是正整数．那么S2001+S2002=多少．
<gadget id="calculator">2_001 + 1</gadget>
<output>2_002</output>

<gadget id="calculator">2_002 / 2</gadget>
<output>1_001</output>

<gadget id="calculator">-1_001</gadget>
<output>-1_001</output>

<gadget id="calculator">1_001 + (-1_001)</gadget>
<output>0</output>

<result>0</result>