$ \text{For } x\in\mathbb{R}, \text{ two real valued functions } f(x) \text{ and } g(x) \text{ are such that } g(x)=\sqrt{x}+1 \text{ and } (f\circ g)(x)=x+3-\sqrt{x}. \text{ Then } f(0) \text{ is equal to: } $