Uniform MLE III

Suppose that $X_1\mid \theta, \dots, X_n \mid \theta \sim \unif{0}{\theta}$ IID. If it exists, find the MLE of $\theta$, $\hat{\theta}_{MLE}$ with the data $\{1,2,3,4,0.5\}$. If it doesn't exist, report $-1$.