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


n = int(input())
items = []
score = 0
for i in range(n):
    temp = list(map(int, input().split()))
    for x in temp:
        if x in items:
            items.remove(x)
            score += 1
        else:
            items.append(x)
score += len(items) // 4
print(score)