How many sodium ions are removed from the crystal, when NaCl is doped with 10-3 mole % of AlCl3 ?

Concentratoin of Al+3 ions=10-3100=10-5      1 mole =6.023×1023Al+3 ions 10-5 mole=.......?                   =10-5×6.023×1023=6.023×1018 One aluminium ion will remove 3 sodium ions to maintain electrical neutrality,hence number of sodium ions removed from crystal =3×6.023×1018