import math
N = int(input())
li = []
match = 0
other = 0
for i in range(N):
    l = list(map(int, input().split()))
    li.extend(l)

for i in range(1,11):
    count = li.count(i)
    match += count / 2
    other += count % 2

print(math.floor(match) + math.floor(other / 4))