import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

N = int(input())
XY = tuple(tuple(map(int, input().split())) for _ in range(N))
dist = []
for i, (x, y) in enumerate(XY):
    for j, (xx, yy) in enumerate(XY):
        if j >= i:
            break
        d = (x - xx) ** 2 + (y - yy) ** 2
        dist.append((d, j, i))


seen = [0] * N
ans = 0
dist.sort()
for _, i, j in dist:
    if seen[i] or seen[j]:
        continue
    if i == 0:
        seen[j] = 1
        ans += 1
    else:
        seen[i] = 1
        seen[j] = 1

print(ans)