def main():
    N = int(input())
    A = [list(map(int, input().split())) for _ in range(N)]
    seen = [0]*N

    task = []
    for i in range(N):
        xi, yi = A[i]
        for j in range(i+1, N):
            xj, yj = A[j]
            d = (xi-xj)**2+(yi-yj)**2
            task.append([d, i, j])

    task.sort(key=lambda x: x[0])
    ans = 0
    for _, indi, indj in task:
        if seen[indi] or seen[indj]:
            continue
        if indi > 0:
            seen[indi] = seen[indj] = 1
        else:
            ans += 1
            seen[indj] += 1

    print(ans)


main()