4. The sequence $\left\{x_{n}\right\}$ is defined as follows:
$$
x_{1}=\frac{2}{3}, x_{n+1}=\frac{x_{n}}{2(2 n+1) x_{n}+1}\left(n \in \mathbf{Z}_{+}\right) \text {. }
$$

Then $x_{1}+x_{2}+\cdots+x_{2014}=$ $\qquad$