Rank of an equi-correlation-type matrix

Let $P = (a_{ij})$ be a $10 \times 10$ matrix with $a_{ij} = \begin{cases} -\frac{1}{10} & \text{if } i \ne j \ \frac{9}{10} & \text{if } i = j \end{cases}$. Then $\operatorname{rank}(P)$ equals