N = int(input())

D = {i:0 for i in range(1,11)}
for _ in range(N):
	li = list(map(int,input().split()))
	for x in li:
		D[x] += 1

ans = 0
amari = 0
for i in range(1,11):
	ans += D[i] // 2
	amari += D[i] % 2

print(ans + amari//4)