CountIF(s) on Merged Cells

Hello,

I will have one of the letters below inputted to a merged cell M8 to P8 - but obviously when I click on them, they are represented by column 'M' as that's the first column I captured when I merged cells.

R
R/A
R/C
R/I
R/A/C
R/A/I
R/C/I
R/A/C/I


I'm trying to write a formula in cell M6 to say: Count only the words used above within the range of M8:M140

How can I write that? I tried something like: =COUNTIFS($M$8:$M$140,"R",$M$8:$M$140,"R/A"...{goes on to cover all 8 words mentioned above}) and it didn't work.

Thank you in advance.

=SUM(COUNTIF(M1:M140,{"r","r/a","r/c","r/i","r/a/c","r/a/i","r/c/i","r/a/c/i"}))