Markov Chains & Long-Run Behavior · Easy problem

A transition matrix is called regular if some power of it has all entries strictly positive. For $M = \begin{pmatrix} 0 & 1/2 \\ 1 & 1/2 \end{pmatrix}$ (columns sum to $1$), what is the smallest positive integer $k$ such that every entry of $M^k$ is positive?