placed = set()
X0 = [(0,9),(1,9),(2,9),(3,9),(4,9),(4,8),(5,8),(5,7),(6,7),
    (7,7),(7,6),(7,5),(8,5),(8,4),(9,1),(9,2),(9,3),(9,4)]
X = X0[:]
for x,y in X0:
    X.append((-x,y))
    X.append((x,-y))
    X.append((-x,-y))
X = set(X)

ans = 0
for _ in range(int(input())):
    x,y = map(int,input().split())
    f = False
    for dx,dy in X:
        if (x+dx,y+dy) in placed:
                f = True
                break
        if f:
            break
    else:
        ans += 1
        for dx,dy in X:
            placed.add((x+dx,y+dy))
print(ans)