2. In a math competition, 3 problems are proposed, each of which is scored with an integer between 0 and 7 (inclusive). It is known that, no matter which two participants are chosen, there is at most one problem on which these two have obtained the same score (for example, there are no two participants whose scores on the three problems are 7, 1, 2 for the first and 7, 5, 2 for the second, but there could be two participants whose scores are 7, 1, 2 and 7, 2, 1). What is the maximum number of participants in the competition?