N = int(input())
item = [list(map(int, input().split())) for _ in range(N)]

box = [0] * 10
for i in item:
    for j in i:
        if j == 1:
            box[0] += 1
        elif j == 2:
            box[1] += 1
        elif j == 3:
            box[2] += 1
        elif j == 4:
            box[3] += 1
        elif j == 5:
            box[4] += 1
        elif j == 6:
            box[5] += 1
        elif j == 7:
            box[6] += 1
        elif j == 8:
            box[7] += 1
        elif j == 9:
            box[8] += 1
        elif j == 10:
            box[9] += 1

revel = 0
amari = 0
for b in box:
    if b >= 2:
        revel = revel + b // 2
        amari = amari + b % 2
    elif b == 1:
        amari += 1
    
print(revel + amari // 4)