Partial Derivatives

Let $f: \mathbb{R}^{10} \rightarrow \mathbb{R}$, where $f = f(x_1,\dots,x_{10})$ is a smooth function (i.e. partial derivatives exist of all orders). How many $5$th order partial derivatives does $f$ have? For example, $\dfrac{\partial f}{\partial x_1^5}$ and $\dfrac{\partial f}{\partial x_1^2 \partial x_2^2 \partial x_6}$ are both $5$th order partial derivatives.