Arrange the first 99 natural numbers in a line from small to large: 12345678910111213...9899, add a plus sign to it, and turn it into an addition formula. If the result is to be the smallest, what is the unit digit of the result.
将前99个自然数从小到大排成一行：12345678910111213…9899，在其中加入一个加号，变成一个加法算式，要使得到的结果最小，那么这个结果的个位数字是多少．
<result>1</result>