A film with a refractive index of 1.4 is coated onto a surface with a refractive index of 1.55. It is desired that the coating does not reflect light with a wavelength of 525 nm. The coating is applied with a thickness exceeding the minimum required to completely eliminate reflection. However, the thickness decreases by 4.2 nm each year due to various reasons. In this situation, what is the maximum number of years for which a guarantee can be provided for the durability of the coating?