MgO crystallizes as rock-salt structure with unit cell length 2.12 Å. From the electrostatic model, the calculated lattice energy in kJ mol$^{-1}$ (rounded off to the nearest integer) is ________.
(Given:} $N_A = 6.022 \times 10^{23}$ mol$^{-1}$, $M = 1.748$, $\varepsilon_0 = 8.854 \times 10^{-12}$ J$^{-1}$C$^2$m$^{-1}$, charge on electron $= 1.602 \times 10^{-19}$ C{)