def lap(bin, x, y, dx, dy):

    cs = []

    cs.extend(bin[dx][dy])
    cs.extend(bin[dx][dy + 1])
    cs.extend(bin[dx][dy + 2])
    cs.extend(bin[dx + 1][dy])
    cs.extend(bin[dx + 1][dy + 1])
    cs.extend(bin[dx + 1][dy + 2])
    cs.extend(bin[dx + 2][dy])
    cs.extend(bin[dx + 2][dy + 1])
    cs.extend(bin[dx + 2][dy + 2])

    for bx, by in cs:
        if (bx - x) ** 2 + (by - y) ** 2 < 400:
            return True

    t = (x, y)
    bin[dx][dy].append(t)
    bin[dx][dy + 1].append(t)
    bin[dx][dy + 2].append(t)
    bin[dx + 1][dy].append(t)
    bin[dx + 1][dy + 1].append(t)
    bin[dx + 1][dy + 2].append(t)
    bin[dx + 2][dy].append(t)
    bin[dx + 2][dy + 1].append(t)
    bin[dx + 2][dy + 2].append(t)

    return False


def solve(XY):
    bin = [[[] for j in range(2003)] for i in range(2003)]

    count = 0
    for x, y in XY:
        dx = x // 10
        dy = y // 10
        if not lap(bin, x, y, dx, dy):
            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()