29. Let $\mathbf{R}_{+}$ denote the set of positive real numbers. Find the function $f: \mathbf{R}_{+} \rightarrow \mathbf{R}_{+}$, such that for all $x, y \in \mathbf{R}_{+}$, we have $f(x f(y))=f(x y)+x$.
(51st Czech and Slovak Mathematical Olympiad (Final))