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