(3+5+7+9+11+...+2003)-(2+4+6+8+10+...+2002)=how much.
(3+5+7+9+11+…+2003)-(2+4+6+8+10+…+2002)=多少．
<gadget id="calculator">2_003 - 3</gadget>
<output>2_000</output>

<gadget id="calculator">2_000 / 2</gadget>
<output>1_000</output>

<gadget id="calculator">2_003 - 2_002</gadget>
<output>1</output>

<gadget id="calculator">1_000 + 1</gadget>
<output>1_001</output>

<result>1_001</result>