Let $\mathbb{N}$ be the set of all natural numbers and $f: \mathbb{N} \rightarrow \mathbb{N}$ be such that $1990 < \mathrm{f}(1990) < 2100$ and satisfies the equation $x-f(x)=19\left[\frac{x}{19}\right]-90\left[\frac{f(x)}{90}\right] \text {, }$ where $[y]$ denotes the greatest integer less than or equal to $y$. Then the number of possible values of $f(1990)$ is