N = int(input())

item = {i + 1:0 for i in range(10)}
for _ in range(N):
    for v in list(map(int, input().split())):
        item[v] += 1

ans = 0

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

ans += sum(v for v in item.values()) // 4
print(ans)