N = input()
items = [0] * 11
for i in range(N):
    for item in map(int, raw_input().split()):
        items[item] += 1
res = 0
for i in range(11):
    res += items[i] / 2
    items[i] = items[i] % 2
rest = sum(items)
res += rest / 4
print res