negation operator with OR condition

Select * from tblPerson
where  (City != 'Chicago' OR City != 'London')

This query should not give the list of cities with Chicago or London names, but it is giving me all the list. I want to know what is wrong with this query and how to fix it.  Also, can we write in this in other way. Please let me know the answer.

Select * from tblPerson

where  City != 'Chicago'  OR  City <> 'London'