With these definitions we obtain the following partial derivatives
\frac{\partial a}{\partial x} = 2x,and
\frac{\partial b}{\partial a} = \exp{a},and
\frac{\partial c}{\partial a} = 1,and
\frac{\partial c}{\partial b} = 1,and
\frac{\partial d}{\partial c} = \frac{1}{2\sqrt{c}},and finally
\frac{\partial f}{\partial d} = 1.