Two horizontal disks freely rotate in different directions around a vertical axis passing through their centers. The masses of the disks are 10 and 40 kg, their radii are 0.2 and 0.1 m, and the angular velocities are 10 and 20 s^-1, respectively. After the fall of the upper disk onto the lower one, both disks, due to the friction between them, began to rotate as a whole after a while. Find the change in the total kinetic energy of the disks.

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