Quantity discount work in a pattern

The merchant wants to set up a repeating tiered discount for a specific product collection, where the discount applies based on the order of items added to the cart, not the specific products.

What they want customers to get:

1st pair → full price

2nd pair → 30% off

3rd pair → 50% off

4th pair → full price (same as 1st)

5th pair → 30% off (same as 2nd)

6th pair → 50% off (same as 3rd)

…and this pattern keeps repeating