The First Derivation Code

The purpose of this code is to make the derivation procedure. This code derivates a function (eg. 12x2+3x to 24x+3, for those who know how to derivate). Well, this is my first code on pscode so I hope you enjoy it. Please vote and/or leave your comments on my code in order to improve it. PD: Sorry for my english, im from Chile. PD: Im thinking on a new update that can work with negative exponents.