def MAX(N, items):
    counts = [0] * 10
    power_ups = 0
    for item_set in items:
        for item in item_set:
            counts[item - 1] += 1
            if counts[item - 1] == 2:
                power_ups += 1
                counts[item - 1] = 0
    total_items = sum(counts)
    power_ups += total_items // 4
    return power_ups
N = int(input())
items = []
for _ in range(N):
    items.append(tuple(map(int, input().split())))
print(MAX(N, items))