In a chess tournament, each player has to play one game with every other player. 2n players, where n is a positive integer, took part in the tournament. so far, player 1 has played 2n - 1 games, player 2 has played 2n - 2 games, player has played 2n - 3 games, and so on until player 2n - 1 has played 1 game. how many games has player 2n played?