# -*- coding: utf-8 -*-

if __name__ == '__main__':
    N = int(input())
    pu_counter = 0
    item_dict = {}
    for i in range(1,11,1):
        item_dict[i] = 0
    for i in range(N):
        items = list(map(int, input().split()))
        for item in items:
            item_dict[item] += 1
    
    # 同一アイテム2個によるパワーアップ
    for i in range(1,11,1):
        pu_counter += item_dict[i] // 2
        item_dict[i] %= 2
    # 4つのアイテムによるパワーアップ
    remainder_sum = 0
    for i in range(1,11,1):
        remainder_sum += item_dict[i]
    pu_counter += remainder_sum // 4

    print(pu_counter)