Biased Coin Puzzle
You and your arch rival are competing for the same girl. After years of battling, you both decide to settle it by tossing a coin.
Your rival produces a coin, but you don't happen to have one on you. You are certain that the coin your rival has produced is loaded, ie. it will come up with heads more than 50% of the time on average.
How do you arrange a fair contest, based purely on chance and not skill, by flipping this coin?