Write a function that calculates the original product price, without VAT.
If a product price is 200.00 and VAT is 15%, then the final product price (with VAT) is: 200.00 + 15% = 230.00
Thus, if your function receives 230.00 as input, it should return 200.00
VAT is always 15% for the purposes of this Kata.
Round the result to 2 decimal places.
If null value given then return -1