how to add 2 to some of array's elements?

I have this array and I would like to add 2 to the elements starting from the third one

a=[1;6;9;8;3;6;8;2;1;5;4;7;6;99;5;4]

so I want to add 2 to 9,8 and 3 up to the end only.

Answer 1

[James Tursa]

a(3:end) = a(3:end) + 2;

[zeezo]

thank you