A parallel plate capacitor is having separation between plates 0.885 mm. It has a capacitance of 1 $$\mu$$F when the space between the plates is filled with an insulating material of resistivity $$1 \times 10^{13}$$ $$\Omega$$m and resistance $$17.7 \times 10^{14}$$ $$\Omega$$. Relative permittivity of the insulating material is $$a \times 10^7$$. The value of $$a$$ is __________. (Take permittivity of free space $$= 8.85 \times 10^{-12}$$ F/m)