What is the sum of all positive fractions whose denominators are not less than 991 and not more than 2010?
所有的分母不小于991、不超过2010的正的真分数的和等于多少．
<gadget id="calculator">2_009 + 1</gadget>
<output>2_010</output>

<gadget id="calculator">2_010 / 4</gadget>
<output>1_005/2 = around 502.5</output>

<gadget id="calculator">2_009 * (1_005/2)</gadget>
<output>2_019_045/2 = around 1_009_522.5</output>

<gadget id="calculator">989 + 1</gadget>
<output>990</output>

<gadget id="calculator">990 / 4</gadget>
<output>495/2 = around 247.5</output>

<gadget id="calculator">989 * (495/2)</gadget>
<output>489_555/2 = around 244_777.5</output>

<gadget id="calculator">(2_019_045/2) - (489_555/2)</gadget>
<output>764_745</output>

<result>764_745</result>