CONO-SUR 1996 Problem 6

Find all integers $n \leq 3$ such that there is a set $S_n$ formed by $n$ points of the plane that satisfy the following two conditions: Any three points are not collinear. No point is found inside the circle whose diameter has ends at any two points of $S_n$ .NOTE: The points on the circumference are not considered to be inside the circle.