Consider the following elements :

$\mathrm{Li}$, $\mathrm{Cs}$, $\mathrm{Mg}$, $\mathrm{Pb}$, $\mathrm{Al}$, $\mathrm{N}$

x = number of elements which can form $\mathrm{MO}$ type of oxides.

y = the highest oxidation state shown by any one of them.

z = the number of elements which can form amphoteric oxide(s).

Find the sum of x, y and z.