Xiao Ming practiced abacus. He started summing from 1 according to the order of natural numbers. When adding to a certain number, the sum was 1000. But he found that one number was missing in the calculation, so how much Xiao Ming missed.
小明练习打算盘，他按照自然数的顺序从1开始求和，当加到某个数时，和是1000，但他发现计算时少加了一个数，那么小明少加了多少．
<gadget id="calculator">45 * 46</gadget>
<output>2_070</output>

<gadget id="calculator">2_070 / 2</gadget>
<output>1_035</output>

<gadget id="calculator">1_035 - 1_000</gadget>
<output>35</output>

<result>35</result>