Hi all, need some advice!

I have the table below with details on the attendance of people at a class.

What I want to do is to add up how many people (ID) have been in attendance anytime in the last 5 months measured from May. Note this is not how many times individuals have attended.

For example

Member ID A was present in Mar, Apr and May

Member ID B was present in Apr, May

Member ID C was present in Apr

Member ID D was present in Mar and May

Member E was not present at all

So the answer for how many members were present in the 5 months of May and previous is 4.

Thanks!