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NL-NWO 2010 Problem 5

    Amber and Brian are playing a game using 20102010 coins. Throughout the game, the coins are divided into a number of piles of at least 1 coin each. A move consists of choosing one or more piles and dividing each of them into two smaller piles. (So piles consisting of only 11 coin cannot be chosen.) Initially, there is only one pile containing all 20102010 coins. Amber and Brian alternatingly take turns to make a move, starting with Amber. The winner is the one achieving the situation where all piles have only one coin. Show that Amber can win the game, no matter which moves Brian makes.

    Dataset text AI-MO AoPS. Quoted with source.

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