In a chess tournament, each contestant plays a match against every other contestant.
Each contestant gets 1 point for every match he wins, 0.5 points for every tied match, and 0 for every game he loses.
At the end of the tournament, it is seen that all competitors got a different number of points and the last competitor in the score ranking defeated each of the top three competitors.
Accordingly, what is the minimum number of competitors participating in the tournament?