def get_observable_positions(x, y):
    directions = [
        (2, -1), (2, 1), (-2, -1), (-2, 1),
        (-1, -2), (1, -2), (-1, 2), (1, 2)
    ]
    observable_positions = set()
    for dx, dy in directions:
        observable_positions.add((x + dx, y + dy))
    return observable_positions

# 入力の読み込み
N = int(input().strip())
umas = [tuple(map(int, input().strip().split())) for _ in range(N)]

uma_positions = set(umas)

# すべての監視装置の配置場所を候補とする
all_positions = set()
for x, y in umas:
    all_positions.update(get_observable_positions(x, y))

# UMAの位置は監視装置を設置できないので除外する
all_positions -= uma_positions

# 監視装置のリスト
all_positions = list(all_positions)

# DFSによるバックトラッキング
def dfs(covered, kma_count, index):
    global min_kma_count
    if kma_count >= min_kma_count:
        return
    if covered == uma_positions:
        min_kma_count = kma_count
        return

    for i in range(index, len(all_positions)):
        new_covered = covered | get_observable_positions(*all_positions[i])
        dfs(new_covered, kma_count + 1, i + 1)

min_kma_count = float('inf')
dfs(set(), 0, 0)

print(min_kma_count)