How to plot a 2 variable piecewise function in Mathematica

Hello I want to plot a sequence of functions (actually just the first few n, say for n=1,2,3).

Given an arbitrary function say a parabloid $\displaystyle f(x,y)=5-(x^2+y^2)$, how can a plot the first few values of the sequence defined below?

$\displaystyle f_n(x,y)=\left\{

\begin{array}{c}

\left.\frac{k}{n},\text{if} f(x,y)\in \left[\frac{k}{n},\frac{k+1}{n}\right.\right), 0\leq k<n. \\

n, \text{if} f(x,y)>n\text{ }

\end{array}

\right.$

Something like a countour plot would be perfect if a 3d is hard to do.