On a smooth horizontal surface is a ball. The second ball weighing 1 kg moves from the vertical wall to the first. Between the balls there is a central elastic impact. What is the minimum value of mass, the first ball is necessary for the second ball to hit the wall after impact and, resiliently reflecting from it, caught up with the first ball? Both balls are on the same perpendicular to the wall.

A detailed solution with a brief description of the condition, formulas and laws used in the solution, the derivation of the formula and the answer.
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