N = int(input())
items = [0] * 100
cnt = 0

for i in range(N):
    for v in input().split():
        idx = int(v)-1
        if items[idx] == 1:
            cnt += 1
            items[idx] &= 0
        else:
            items[idx] |= 1

cnt += items.count(1)//4
print(cnt)