Does anyone have any suggestion on how to count the matched values?

There is a list of values under column A & B
[Column A] 1,5,6,8,9,10,3,20
[Column B] 6,4,9

I would like to count the number of values in column B, which is matched any
value in column A. In this case, the matched values are 6 & 9, and it will
return 2 in cell C1.
Does anyone have any suggestions?
Thank you for any suggestions
Eric