Seek 1991*1991-1990*1990=?
求1991*1991-1990*1990=？
<gadget id="calculator">1_990 * 1_991</gadget>
<output>3_962_090</output>

<gadget id="calculator">1_990 * 1_990</gadget>
<output>3_960_100</output>

<gadget id="calculator">1_991 - 3_960_100</gadget>
<output>-3_958_109</output>

<gadget id="calculator">3_962_090 + (-3_958_109)</gadget>
<output>3_981</output>

<result>3_981</result>