2003*2003+2004*2004-2003*2004-2002*2003=how much.
2003*2003+2004*2004-2003*2004-2002*2003=多少．
<gadget id="calculator">2_003 * 2_003</gadget>
<output>4_012_009</output>

<gadget id="calculator">2_004 * 2_004</gadget>
<output>4_016_016</output>

<gadget id="calculator">2_003 * 2_004</gadget>
<output>4_014_012</output>

<gadget id="calculator">2_002 * 2_003</gadget>
<output>4_010_006</output>

<gadget id="calculator">4_016_016 - 4_014_012 - 4_010_006</gadget>
<output>-4_008_002</output>

<gadget id="calculator">4_012_009 + (-4_008_002)</gadget>
<output>4_007</output>

<result>4_007</result>