Discount based on multiples of x

[Evildood]

I am struggling to set up a discount in Prestashop 1.6.1.1, I have been looking on Youtube and the net for the last couple of hours and cannot for the life of me find a solution, so if anyone can help, I would appreciate it :-

 

Basically I want to have a discount applied to a multiple of 4 products

 

e.g. if someone orders 3 bottles of aftershave at £5.00 ea. then the price would be £15, but if someone orders 4 bottles then a discount of £2.00 would be applied, therefore 4 bottles would automatically be calculated at £18. easy enough to do that, but I want the discount to apply to multiples of 4 so if someone ordered 5 bottles, they would pay £18 for the first 4 and £5 for every additional bottle less than an additional 4.

 

e.g.

 

1 = £5

2 = £10

3 = £15

4 = £18

 

5 = £23

6 = £28

7 = £33

8 = £36

 

Is there anyway I can do this within vanilla Prestashop?, if not does anyone know of an addon that could do this?

 

or if you have a suggestion or work around I would appreciate your input.

 

Thanks.

 

[Evildood]

Anyone got any ideas or suggestions?, even if you can point me in the right direction.

 

Thanks.