lib C
  fun strtoll(s : UInt8*, p : UInt8**, b : Int32) : Int64
end

class String
  def to_i64
    C.strtoll(self, nil, 10)
  end
end

n = read_line.to_i
x, y = (1..n).map { read_line.split.map(&.to_i64) }.transpose
dist = (0...n).flat_map { |i|
  (i + 1...n).map { |j|
    {(x[i] - x[j])**2 + (y[i] - y[j])**2, i, j}
  }
}.sort

flag = [true] * n
ans = 0
dist.each do |(d, i, j)|
  if flag[i] && flag[j]
    if i == 0
      ans += 1
      flag[j] = false
    else
      flag[i] = false
      flag[j] = false
    end
  end
end
puts ans