count duplicates in groups of 4

[alexbotea2005]

Hi,
I need some help with vba macro.
I have a table where column B has series of duplicate values. I need to count those duplicates in groups of 4 (column H) and then assign a group index on column I.
The index value will be 1 for most of the groups unless the group is duplicate.
My initial trial was to number the duplicates inside the group, but after this I’m stuck.
Thanks in advance for you help.