loop do
  n = gets.to_i
  break if n.zero?
  ps = n.times.map { x, y = gets.split(?,).map(&:to_f); x + y * 1i }
  p0 = ps.min_by(&:imag)
  p, u, c = p0, 1, 1
  loop do
    q = ps.reject {|q| p == q }.min_by {|q|
      v = q - p
      a = (v / u).arg
      a < 0 ? 2 * Math::PI + a : a
    }
    break if q == p0
    c += 1
    u = q - p
    u /= u.abs
    p = q
  end
  p ps.size - c
end