class Point
  include Comparable
  attr_accessor :x, :y
  def initialize(x=0.0, y=0.0)
    @x, @y = x, y
  end
  def <=>(p)
    @y != p.y ? @y <=> p.y : @x <=> p.x
  end
  def +(p)
    Point.new(@x+p.x, @y+p.y)
  end
  def -(p)
    Point.new(@x-p.x, @y-p.y)
  end
  def -@
    Point.new(-@x, -@y)
  end
  def angle
    a = Math::atan2(@y, @x)
  end
end

while (n = gets.to_i) != 0 do
  point = Array.new
  n.times do
    point.push(Point.new(*(gets.split(",").map(&:to_f))))
  end
  point.sort!

  convexHull = Array.new
  convexHull.push(point.first)
  convexHull.push(point.drop(1).min_by{|p| (p-point.first).angle})
  while true do
    origin = convexHull.last
    base = (convexHull[-1] - convexHull[-2]).angle
    add = nil
    min = 2.0 * Math::PI
    point.each do |p|
      next if origin == p
      angle = (p-origin).angle - base
      angle += 2.0 * Math::PI if angle < 0.0
      next if min <= angle
      min = angle
      add = p
    end
    break if convexHull.first == add
    convexHull.push(add)
  end
  p n - convexHull.size
end