N = int(input()) A = [] for _ in range(N): A += list(map(int, input().split(' '))) K = {1 : 0, 2 : 0, 3 : 0, 4 : 0, 5 : 0, 6 : 0, 7 : 0, 8 : 0, 9 : 0, 10 : 0} for i in A: if i in K: K[i] += 1 level = 0 for i in range(1, 11): level += K[i] // 2 W = (N * 3 - level * 2) // 4 R = W + level print(R)