from collections import defaultdict


def main():
    N = int(input())
    cards = [list(map(int, input().split())) for _ in range(N)]
    cards_num = defaultdict(int)
    for (card_n, v) in cards:
        cards_num[card_n] += v

    multi_8_num = sum(
        cards_num[card_n] for card_n in filter(
            lambda card_n: card_n %
            8 == 0, cards_num))
    multi_4_num = sum(
        cards_num[card_n] for card_n in filter(
            lambda card_n: card_n %
            4 == 0 and card_n %
            8 != 0, cards_num))
    multi_2_num = sum(
        cards_num[card_n] for card_n in filter(
            lambda card_n: card_n %
            2 == 0 and card_n %
            4 != 0, cards_num))

    ans = multi_8_num

    used = min(multi_2_num, multi_4_num)
    ans += used

    multi_2_num -= used
    multi_4_num -= used

    ans += multi_4_num // 2
    ans += multi_2_num // 3

    print(ans)


if __name__ == "__main__":
    main()