How to complete this task?

Question

C++ / C#

Problem 6.3 Write a program to solve the following problem: Using
the expansion formula, calculate the value of the number π with a given accuracy d = 0.001. as a
reference, use the value Pi = 3.14159. Calculations are carried out until the difference between the reference and calculated value of π modulo becomes less than the specified accuracy.
- decomposition formula.
I don't understand how to solve this at all.

Answer 1

Calculate the expression in brackets for a finite number N, get the result of the entire formula.
Calculate the result for N + 1. Compare with the previous one, make sure they match up to the third decimal place. If not, keep increasing N until the condition is met.
It will take a couple of cycles and a little math.

Answer 2

You make a loop in which you get a number, add it to the previous calculated one, round up to x.xxx and compare with Pi rounded up to x.xxx
If it matches, you stop the loop.