Xiao Wang is doing addition operations. He starts from the natural number 1 and sums in ascending order: 1+2+3+4+... When adding to a certain number, the "sum" he gets is 1500, but he finds that In the process of adding, a two-digit number is missing, so what is the missing number?
小王在做加法运算，他从自然数1开始，按从小到大的顺序求和：1+2+3+4+…，当加到某个数时得到的"和"是1500，但是他发现在加的过程中少加了一个两位数，那么这个被少加的数是多少
<gadget id="calculator">55 ** 2</gadget>
<output>3_025</output>

<gadget id="calculator">3_025 + 55</gadget>
<output>3_080</output>

<gadget id="calculator">3_080 / 2</gadget>
<output>1_540</output>

<gadget id="calculator">1_540 - 1_500</gadget>
<output>40</output>

<result>40</result>