A tennis player computes her win ratio by dividing the number of matches she has won by the total number of matches she has played. At the start of a weekend, her win ratio is exactly $$.500$$. During the weekend, she plays four matches, winning three and losing one. At the end of the weekend, her win ratio is greater than $$.503$$. What's the largest number of matches she could've won before the weekend began?

(第一十届AIME1992 第3题)