Method of moments for a symmetric discrete uniform

Let $x_1=-2,x_2=1$ and $x_3=-1$ be the observed values of a random sample of size three from a discrete distribution with the probability mass function

$$f(x;\theta)=P(X=x)=\begin{cases}\dfrac1{2\theta+1}, & x\in\{-\theta,-\theta+1,…,0,…,\theta\},\ 0, & \text{otherwise,}\end{cases}$$

where $\theta\in\Theta=\{1,2,…\}$ is the unknown parameter. Then the method of moment estimate of $\theta$ is