import collections

n = int(input())
itm = []
for i in  range(n):
   itm += (list(map(int, input().split())))

c = collections.Counter(itm)


p_1 = sum([ c[i]//2 for i in c if c[i]%2==0 ])

p_2 = sum([ c[i]//2 for i in c if c[i]%3==0 ])

p_3 = sum([ c[i]%2 for i in c if c[i]%3==0 ])
p_4 = sum([ c[i] for i in c if c[i]==1 ])
p_5 = (p_3 + p_4)//4

print(p_1 + p_2 + p_5)