Xiao Li practiced calculations with an abacus. He summed the natural numbers from 1 in the order of the natural numbers. When adding to a certain number, the sum was 1997. But he found that he added one less number during the calculation, so how much he added less.
小李练习用算盘计算，他按照自然数的顺序从1开始求和，当加到某个数时，和是1997，但他发现计算时少加了一个数，那么他少加了多少．
<gadget id="calculator">2_008 - 1_997</gadget>
<output>11</output>

<result>11</result>