Clever calculation: 2015+2014+...+2+1.
巧算：2015+2014+…+2+1．
<gadget id="calculator">2_015 + 1</gadget>
<output>2_016</output>

<gadget id="calculator">2_015 / 2</gadget>
<output>2_015/2 = around 1_007.5</output>

<gadget id="calculator">2_016 * (2_015/2)</gadget>
<output>2_031_120</output>

<result>2_031_120</result>