Consistent estimator for the scale of a quartic-type density

Let $X_1,…,X_n$ be a random sample from a population with probability density function

$$f_\theta(x)=\begin{cases}\frac4\theta x^3e^{-x^4/\theta}, & x>0,\ 0, & \text{otherwise,}\end{cases}$$

where $\theta>0$ is unknown. Then, a consistent estimator for $\theta$ is