Number of minima and maxima of a scalar function in $\mathbb R^3$

Question

Given a continuous (if need be $C^\infty$) function $\Phi(\boldsymbol{x})$, mapping $\mathbb{R}^3\to\mathbb{R}$, that has $n$ minima and obtains $\Phi\to0$ for $|\boldsymbol{x}|\to\infty$, is there a theorem about the number $m$ of maxima and/or saddles, i.e. points (apart from the minima) where $\boldsymbol{\nabla}\Phi=0$?