n = gets.to_s.to_i
xy = Array.new(n){ gets.to_s.split.map { |v| v.to_i64 - 1} }

dists = [] of Tuple(Int64,Int32,Int32)
n.times do |i|
  n.times do |j|
    next unless i < j
    xi,yi = xy[i]
    xj,yj = xy[j]
    dist = (yi - yj) ** 2 + (xi - xj) ** 2
    dists << {dist, i, j}
  end
end

bang = Array.new(n, false)
ans = 0_i64
dists.sort.each do |d, i, j|
  next if bang[i] || bang[j]
  if i == 0
    bang[j] = true
    ans += 1
  else
    bang[i] = true
    bang[j] = true
  end
end
puts ans