Figure (8-E15) shows a smooth track, a part of

Figure (8-E15) shows a smooth track, a part of which is a circle of radius $\mathrm{R}$. A block of mass $m$ is pushed against a spring of spring constant $\mathrm{k}$ fixed at the left end and is then released. Find the initial compression of the spring so that the block presses the track with a force mg when it reaches the point $\mathrm{P}$, where the radius of the track is horizontal.