Calculation: 1999*1998-1997*1996=how much.
计算：1999*1998-1997*1996=多少．
<gadget id="calculator">1_999 * 1_998</gadget>
<output>3_994_002</output>

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

<gadget id="calculator">3_994_002 - 3_986_012</gadget>
<output>7_990</output>

<result>7_990</result>