N = int(input())

x = [0] * 10

ans = 0
for i in range(N):
    a = map(int, input().split())
    for t in a:
        x[t-1] += 1
        d, x[t-1] = divmod(x[t-1], 2)
        ans += d
ans += sum(x) // 5
print(ans)