from collections import defaultdict


def lap(bin, x, y, dx, dy, xx, yy):
    for xxx in xx:
        for yyy in yy:
            for bx, by in bin[dx + xxx, dy + yyy]:
                if (bx - x) ** 2 + (by - y) ** 2 < 400:
                    return True

    for xxx in xx:
        for yyy in yy:
            bin[dx + xxx, dy + yyy].append((x, y))
    return False


def solve(XY):
    bin = defaultdict(list)

    count = 0
    for x, y in XY:
        dx, mx = divmod(x, 20)
        dy, my = divmod(x, 20)

        xx = [0]
        if mx < 10:
            xx.append(-1)
        elif mx > 10:
            xx.append(1)

        yy = [0]
        if my < 10:
            yy.append(-1)
        elif my > 10:
            yy.append(1)

        if not lap(bin, x, y, dx, dy, xx, yy):
            count += 1

    return count


def main():
    N = int(input())
    XY = [list(map(int, input().split())) for i in range(N)]

    print(solve(XY))


if __name__ == '__main__':
    main()