Structure of Atom Part 1

The longest wavelength of light that can be used for the ionisation of lithium atom (Li) in its ground state is x×10−8m. The value of x is___ (Nearest Integer).
(Given : Energy of the electron in the first shell of the hydrogen atom is −2.2 ×10−18J;h=6.63×10−34‌Js and c=3×108ms−1 )