n = int(input())

item = [0] * 11
for _ in range(n):
    mp = map(int, input().split())
    for e in mp:
        item[e] += 1

ans = 0
for i in range(1, 11):
    q, item[i] = divmod(item[i], 2)
    ans += q

ans += sum(item) // 4
print(ans)