No of rotational directors.

2/3rd i.e.10 should be rotational and out of these 10 atleast 4 should retire every year.
refer section 152(6).

As per section 152(6), 2/3rd director of total no. of director shall be appointed on Retire by rotation basis and remaining 1/3rd directors on non rotational basis. And 1/3rd directors out of 2/3rd who is appointed on rotational basis shall retire at every AGM and those who have been longest in office shall retire first.