Computing the limit of the sequence

Given a real number a, we want to compute the limit of the sequence:

x1 = x - (x^3 - a) / (3x^2)

where the initial value of x is a. Start by setting x=a and computing the right-hand side. The result will be the next value of x.

Create the app that uses 0.001 as tolerance, reads a, and outputs the limit. The app stops iterating when the absolute value of the difference between the old and new values of x becomes less than the tolerance.

anyone can help me with this?