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The characteristic equation of a unity negative feedback system is $1+KG(s)=0$. The open loop transfer function $G(s)$ has one pole at $0$ and two poles at $-1$. The root locus of the system for varying $K$ is shown in the figure.

The constant damping ratio line, for $\xi = 0.5$, intersects the root locus at point A. The distance from the origin to point A is given as $0.5$. The value of $K$ at point A is ________.