def main():

    encounter_enemy = int(input())
    get_items = [list(map(int, input().split())) for _ in range(encounter_enemy)]
    get_items_list = []
    same_items_count_list = []
    same_items_power_up_list = []

    #手にいれたアイテム全てを一つのリストに
    for item in get_items:
        for i in item:
            get_items_list.append(i)

    item_sorts = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    #1~10までの種類のアイテムの個数をリストで表示
    for same_items in item_sorts:
        same_items_count = get_items_list.count(same_items)
        same_items_count_list.append(same_items_count)

    #同じ種類のアイテムでパワーアップする回数
    for s in same_items_count_list:
        same_items_change_power = s // 2
        same_items_power_up_list.append(same_items_change_power)
    same_items_power_up = sum(same_items_power_up_list)

    #残ったアイテムでパワーアップする回数
    leftovers = len(get_items_list) - (same_items_power_up * 2)
    leftovers_power_up = leftovers // 4

    #最終的にパワーアップする回数
    power_up_count = leftovers_power_up + same_items_power_up
    print(power_up_count)


if __name__ == '__main__':
    main()