The Elo rating system is a method for calculating the relative chess skill levels of players in competitor-versus-competitor games. ( http://en.wikipedia.org/wiki/Elo_rating_system )
The difference in the ratings (rating=ELO) between two players serves as a predictor of the outcome of a match. Two players with equal ratings who play against each other are expected to score an equal number of wins. A player whose rating is 100 points greater than their opponent's is expected to score 64%; if the difference is 200 points, then the expected score for the stronger player is 76%.
Some chess organizations use the "algorithm of 400" to calculate performance rating. According to this algorithm, performance rating for an event is calculated by taking (1) the rating of each player beaten and adding 400, (2) the rating of each player lost to and subtracting 400, (3) the rating of each player drawn, and (4) summing these figures and dividing by the number of games played.
Find the performance with this algorithm with ELO players and results (0=loss,0.5=draw,1=win) in input.