There are \(2015\) cards lying on a table. Some of them are face-up while the others are face-down. A move consists of turning over some of the cards. However, you are allowed to flip exactly \(n\) cards in the \(n\)-th move.
Prove that it is possible to turn over the cards in such a way that after the \(2015\)th move, all the cards are either face-up or face-down.
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