Left inverse of a function

Question

Let $f$ be the function $f\colon \mathbb{N}\rightarrow\mathbb{N}$, defined by rule $f(n)=n^2$.

Needed to find two left inverse functions for $f$. I know only one: it's $g(n)=\sqrt{n}$. Does anyone can help me to find second left inverse function?

Answer 1

Note that $\sqrt n$ is not always an integer, so this is not the correct function, because its range is not the natural numbers.

Hint: You can round a non-integer up and down.