0 = (\delta f \frac{\partial (F+G)}{\partial f'})_{r=0}^{R} + (\delta f' \frac{\partial G}{\partial f''}))_{r=0}^{R} - (\delta f \frac{d}{dr}\frac{\partial G}{\partial f''})_{r=0}^{R} + \int dr (\frac{\partial F}{\partial f} + \frac{\partial G}{\partial f} + 2\pi r p -  \frac{d}{dr}(\frac{\partial F}{\partial f'}) - \frac{d}{dr}(\frac{\partial G}{\partial f'}) + \frac{d^2}{dr^2}(\frac{\partial G}{\partial f''}))\delta f