Description

According to the formula:
$arctan(x) = x - \frac{x^3}{3} + \frac{x^5}{5} - \frac{x^7}{7} + ...$
and
$\pi = 6 \cdot arctan\left(\frac{1}{\sqrt{3}}\right)$,
define the function $arctan(x)$ and compute the value of $\pi$ when the last term is less than $10^{-6}$.

Input Format

(None)

Output Format

The value of $\pi$, rounded to 10 decimal places.

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