from collections import Counter
N = int(input())
items = [input().split() for x in range(N)]
number = [str(i) for i in range(1,11)]
cnt = Counter()
for item in items:
    cnt.update(item)
a, b = 0, 0
for n in number:
    i2, i1 = divmod(cnt[n], 2)
    a += i2
    b += i1
print(a+b//4)