need help on this while loop as well in Matlab

Another less efficient way to estimate pi is the Gregory-Leibniz series pi 4/1-4/3 + 4/5-4/7 + 4/9 Use a while loop to approximate pi using this technique (5 points). Continue the calculations until the absolute value of the difference between the value of pi stored in MATLAB and the approximation is less than 0.001. Report the final approximation and the number of iterations required (5 points). Hint: to alternate the sign on each term use (-1) raised to a power