placed = set()
X = [19, 19, 19, 19, 19, 19, 19, 18, 18, 17, 17, 16, 15, 15, 14, 13, 11, 10, 8, 6]
W = 20100
for _ in range(int(input())):
    x, y = map(int, input().split())
    x += 20
    y += 20
    f = False
    for dx in range(-19, 20):
        i = abs(dx)
        for dy in range(-X[i], X[i] + 1):
            if (x + dx) * W + y + dy in placed:
                f = True
                break
        if f:
            break
    else:
        placed.add(x * W + y)
print(len(placed))