from collections import Counter
ans=0
items,x=[],[]
for _ in '1'*int(input()): 
	items.extend(list(map(int, input().split())))
for [i, j] in Counter(items).most_common():
	if j > 1:
		ans += int(j/2)
		x.append(j%2)
	else:
		x.append(i)
ans += int(len(x)/4)
print(ans)