Does anyone know on how to determine the value in following case?

In cell A1 = 10 In cell B1 = 12
In cell A2 = 15 In cell B2 = 17
In cell A3 = 20 In cell B3 = 23

I would like to determine which pair [A & B] will be the minimum difference,
let take the abs of the difference in order to avoid negvative results. In
this case, abs(12-10) = 2 and abs(17-15) = 2, there are 2 pairs of value to
meet the minimum difference between A & B columns. Then I would like to
determine the minimum median value from those pairs, in this case (12+10) =
11, then the 11 will display in cell C1. Does anyone have any suggestion on
how to do this calculation in excel?
Thank you in advance
Eric Choi