In a radar chart (spider plot) with 5 axes, each axis represents a variable $v_i \in [0, 10]$. The area of the polygon formed by connecting points $(r_1, \theta_1), ..., (r_5, \theta_5)$ is given by $\frac{1}{2} \sum r_i r_{i+1} \sin(\frac{2\pi}{n})$. If all $r_i = 5$, what is the area?