A player $\mathrm{X}$ has a biased coin whose probability of showing heads is $\mathrm{p}$ and a player $\mathrm{Y}$ has a fair coin. They start playing a game with their own coins and play atlernately. The player who throws a head first is a winner. If X starts the game, and the probability of winning the game by both the players is equal, then the value of ' $p$ ' is :-