So, you're just trying to calculate the number of items to place into 2 separate columns based on the total number of items? And, with an even number of items, each column should have the same number of items and with an odd number of items, the left-hand column should have 1 more?
If so, something like this should work:
var total_items = 11
var left = ceil(float(total_items) / 2)
var right = total_items - left