UMVUE of theta squared for a Pareto

Let $X_1,X_2,X_3,X_4$ be a random sample from a continuous distribution with probability density function $$f(x;\theta)=\begin{cases}2\theta^2 x^{-3}& \text{if }\theta<x<\infty,\ 0& \text{otherwise,}\end{cases}$$ where $\theta>0$ is an unknown parameter. It is known that $X_{(1)}=\min\{X_1,X_2,X_3,X_4\}$ is a complete sufficient statistic for $\theta$. If the observed values are $x_1=15$, $x_2=11$, $x_3=10$, $x_4=17$, the uniformly minimum variance unbiased estimate of $\theta^2$ is equal to __________ (answer in integer)