N = int(input())
power_up = []
count = 0
for i in range(N):
    items = list(map(int, input().split()))
    for item in items:
        if item in power_up:
            power_up.remove(item)
            count += 1
        else:
            power_up.append(item)
if len(power_up) >= 4:  
    while len(power_up) >= 4:
        del power_up[:4]
        count += 1

print(count)