The position $x(t)$ of a particle, at constant $\omega$, is described by the equation
$$\frac{d^2 x}{d t^2}=-\omega^2 x.$$
The initial conditions are $x(t=0)=1$ and $\left.\frac{d x}{d t}\right|_{t=0}=0$. The position of the particle at $t=(3 \pi / \omega)$ is_______________(in integer).