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 matched value between both columns, but
I would like to set an range [+/- 1] for each values in column B. The set
value 1 is inputed in cell D1. Such as 4 will not be found in column A, but
after the range applied to value 4, if any number is found in column A
between 3 [4-1] and 5 [4+1], then it should belong to matched value.
The matched values are 6, 4 and 9, and it will return 3 in cell C1.
Does anyone have any suggestions on how to do it?

Thanks in advance for any suggestions
Eric