Two players X and O play a game of "doughts and crosses" on a 3 x 3 grid. The purpose of the game is for a player to get 3 symbols belonging to the player in a straight line (vertically, horizontally or diagonally). Each player marks one symbol on his or her turn. After two moves (1 turn each), the grid looks as follows with X to play next.
Where should X put his symbol next so that he will always win this game finally regard less of how well O plays ?