N = int(input())
zahyo = [tuple(map(int, input().split())) for _ in range(N)]
records = []
for i in range(N):
    xi, yi = zahyo[i]
    for j in range(i + 1, N):
        xj, yj = zahyo[j]
        d = (xi - xj)**2 + (yi - yj)**2
        records.append((d, i, j))

done = [False] * N
records.sort(key=lambda x: x[0])
ans = 0
for d, i, j in records:

    if done[i] or done[j]:
        continue

    if i == 0:
        ans += 1
        done[j] = True

    else:
        done[i] = True
        done[j] = True
print(ans)