3. Given the sequence $\left\{a_{n}\right\}$ satisfies $a_{1}=1, a_{n+1}=n+1+a_{n}\left(n \in \mathbf{N}^{*}\right)$, if $[x]$ represents the greatest integer not exceeding the real number $x$, then $\left[\frac{1}{a_{1}}+\frac{1}{a_{2}}+\cdots+\frac{1}{a_{2018}}\right]=(\quad)$
A: 1
B: 2
C: 3
D: 2018
Rong's Problem A.
Parse $\because \sum_{k=1}^{n-1}\left(a_{k+1}-a_{k}\right)=\sum_{k=1}^{n-1}(k+1), \therefore a_{n}-a_{1}=\frac{n(n+1)}{2}-1 \Rightarrow \frac{1}{a_{n}}=\frac{2}{n(n+1)}$, so
$$
\left[\sum_{k=1}^{2018} \frac{1}{a_{k}}\right]=\left[2\left(1-\frac{1}{2019}\right)\right]=2
$$