Evaluation of Nested Piecewise Functions

Consider the function defined by the piecewise expression:

$$ f(x) = \begin{cases} 2x + 3 & \text{if } x < 1 \\ 5 & \text{if } x = 1 \\ x^2 - 1 & \text{if } x > 1 \end{cases} $$

What is the value of $$ f(f(0)) $$?