Consider a Boolean function \( f(w,x,y,z)\) such that <span…

Consider a Boolean function $f(w,x,y,z)$ such that

<span class="mathjax-latex">$\begin{array}{lll} f(w,0,0,z) & = & 1 \\ f(1,x,1,z) & =& x+z \\ f(w,1,y,z) & = & wz +y \end{array}$</span>

The number of literals in the minimal sum-of-products expression of $f$ is _________ .