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

    item_sorts = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

    for same_items in item_sorts:
        same_add_power = get_items_list.count(same_items)
        same_items_count_list.append(same_add_power)
    #1~10までのアイテムの個数をリストで表示
    # print(same_items_count_list)
    for add_power in same_items_count_list:
        a = add_power // 2
        same_items_power_up.append(a)
    # print(same_items_power_up)
    #同じアイテムが二つでパワーアップの条件でパワーアップする量
    # print(sum(same_items_power_up))

    # print(len(get_items_list))
    b = len(get_items_list) - (sum(same_items_power_up * 2))
    c = b // 4
    # print(c)
    print(c + sum(same_items_power_up))
    # print(b)

    

# power_up_count = []

if __name__ == '__main__':
    main()