Calculate with a simple method: 2000*1999-1999*1998+1998*1997-1997*1996.
用简便方法计算：2000*1999-1999*1998+1998*1997-1997*1996．
<gadget id="calculator">2_000 * 1_999</gadget>
<output>3_998_000</output>

<gadget id="calculator">1_999 * 1_998</gadget>
<output>3_994_002</output>

<gadget id="calculator">3_998_000 - 3_994_002</gadget>
<output>3_998</output>

<gadget id="calculator">1_998 * 1_997</gadget>
<output>3_990_006</output>

<gadget id="calculator">1_997 * 1_996</gadget>
<output>3_986_012</output>

<gadget id="calculator">3_990_006 - 3_986_012</gadget>
<output>3_994</output>

<gadget id="calculator">3_998 + 3_994</gadget>
<output>7_992</output>

<result>7_992</result>