Write a function that calculates the original product price, without VAT.
## Example
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`
**Notes:** 
* VAT is *always* `15%` for the purposes of this Kata.
* Round the result to 2 decimal places.
* If `null` value given then return `-1`
excluding_vat_price = lambda p: round(p/115*100, 2) if p else -1
excluding_vat_price = lambda p: round(p/115*100, 2) if p else -1