n = int(raw_input())
items = [0 for _ in range(10)]
for _ in range(n):
	for i in map(int,raw_input().split()):
		items[i-1] += 1
cnt = 0
for i in range(10):
	p = items[i]/2
	if p > 0:
		cnt += p
		items[i] -= p*2
else:
	if sum(items)/4 > 0:
		cnt += sum(items)/4
print cnt