The first line of the input file contains a single integer — the number of watchtowers. The next lines of the input file contain the Cartesian coordinates of watchtowers, one pair of coordinates per line. Coordinates are integer and do not exceed by absolute value. Towers are listed in the order of traversal of their convex hull in clockwise direction.
输出格式
Write to the output file the number of watchtowers the enemy has to blow up to compromise headquarters protection if the headquarters are placed optimally.
