import strutils, sequtils

const
  M = 20001
  LEN = 33
  CNT = M div LEN

type
  Point = tuple[x,y:int]

###
# (ΦωΦ)＜もっといい方法はないかな？
proc mymapII(s:seq[string]):auto= result = (s[0].parseInt, s[1].parseInt)
###

var
  n = stdin.readLine.parseInt
  blocks:seq[seq[seq[Point]]] = newSeqWith(CNT+1, newSeqWith(CNT+1, newSeq[Point](0)))
  res = 0

for i in 0.. <n:
  var (x, y) = stdin.readLine.split.mymapII
  var px = x div LEN
  var py = y div LEN
  var ok = true
  for xx in -1..1:
    for yy in -1..1:
      var nx = px + xx
      var ny = py + yy
      if nx < 0 or CNT < nx or ny < 0 or CNT < ny: continue
      for p in blocks[nx][ny]:
        if (p.x-x)*(p.x-x) + (p.y-y)*(p.y-y) < 400:
          ok = false
          break
  if ok:
    res += 1
    var point:Point = (x: x, y: y)
    blocks[px][py].add(point)

echo res