n = int(input())
items = [j for i in [list(map(int, input().split())) for _ in range(n)] for j in i]
counter = [items.count(i) for i in range(1, 11)]

pc = 0
for i, c in enumerate(counter):
    pc += c // 2
    counter[i] %= 2

pc += sum(counter) // 4
print(pc)