N = int(input())
L = [0 for i in range(11)]

for _ in range(N):
    I = map(int, input().split())
    for i in I:
        L[i] += 1

cnt = 0
for i in range(11):
    if L[i] > 1:
        cnt += L[i] // 2
        L[i] %= 2
cnt += sum(L) // 4

print(cnt)