difference between numbers in a rolling series

trying to figure out a formula to be able to do the following
for ease of example we will say set of numbers between 1 to 20
I want excel to look at this as a rolling series ie.

1.2.3.4.5.6.7.8.9,10,11,12,13,14,15,16,17,18,19,20,1,2,3,4,5,6,7,8,9,10 etc

column 1 column 2- positive difference between outcomes ie use this i think is right =IF(A2>A1,+A2-A1,A1-A2) please correct if this is wrong
numbers

10 ( 8 )
16 ( 6 )
13 ( 3 )
18 ( 5 )
4 ( 6 ) this is were i am stuck i want this to be displayed as the shorter distance ie not 14 but 6 - ie no difference should be greater than 10
5 ( 1 )
etc

any help would be appreciated, please ask if clarification is needed
thanks in advance