How I can pair two cells that have the same value in different columns

I apologize in advance for my poor English.

How I can pair cells from different columns based on the same (exact) value (number).
Similar numbers are repeated in both columns, but I need to write in column C which number from column B has its pair anywhere in column A.
The table is large and can be several hundred pairs.

example3.jpg

One pair = one unpaired number anywhere in column B and the first same unpaired number from top to bottom in column A.

As a rule, each number from column A will be paired with the number in column B, but not every number from column B will be paired with the number in column A. Column B will contain more numbers (row) than column A.