I came across the problem that says:
Find the set of all limit points of the set $S=\left\{n+\frac{1}{3m^{2}};\,n,m \in \mathbb N\right\}$. There are four options:
(a) $\mathbb{Q}$.
(b) $\mathbb{Z}$.
(c) $\mathbb{R}$.
(d) $\mathbb{N}$.
Could someone point me in the right direction? Thanks in advance for your help.