Macro to insert a column and fill that column with word "January"

Hi Can anyone please help?

I need a macro so that it inserts a column between column A & B and then all cells in new column filled by word "January".

I tried recording macro but the problem is that it fills all cell in column B upto cell B65000. I need to fill cell only upto where there's data on column A so if column A has data upto 6000 then only upto B6000.

Any help much appreciated.