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)
    if count >= 2:
        match += math.floor(count / 2)
        other += count % 2
    else:
        other += count

print(int(match + (other / 4)))