When the board of directors consists of two or more members, in lieu of electing the whole number of directors annually, the articles of incorporation may provide that the directors be divided into either two or three classes, each class to be as nearly equal in number as possible, the term of office of directors of the first class to expire at the first annual meeting of shareholders after their election, that of the second class to expire at the second annual meeting after their election and that of the third class, if any, to expire at the third annual meeting after their election. At each annual meeting after the classification, the number of directors equal to the number of the class whose term expires at the time of the meeting shall be elected to hold office until the second succeeding annual meeting, if there are two classes, or until the third succeeding annual meeting, if there are three classes. No classification of directors shall be effective prior to the first annual meeting of shareholders.