i1 = int(input())
i2 = []
for _ in range(i1):
    i2.extend(list(map(int,input().split())))
    
rest = i2; cps = 0
for i in range(1,11):
    n = i2.count(i)
    if n // 2 > 0:
        cps += n // 2
        for _ in range(n - n % 2):
            rest.remove(i)

quin = len(rest) // 4
print(cps + quin)