A cube of wood of mass 0.5 kg and density 800 kg m-3 is fastened to the free end of a vertical spring of spring constant k= 50Nm-1, fixed at the bottom. Now, the entire system is completely submerged in water. The elongation or compression of the spring in equilibrium is β2 cm. The value of β is __. (Given, g= 10 ms-2)