Polygon#151
A military training ground is shaped as an -gon (a polygon with vertices). It is known that if exactly one vertex is removed, the resulting polygon becomes convex. Find the index of this vertex.
The first line contains (4 \leq n \leq 20).
Each of the following lines contains two integers, the coordinates of the -th vertex in order.
Vertices are numbered from to in the order they are given.
Print the index of the vertex to remove so that the resulting polygon is convex.
Example 1