N = input()
AA = []
for i in range(0,N):
    AA.extend(list(map(int,raw_input().split())))
cnt,nokori = 0,0
for i in range(1,N+1):
    if AA.count(i)%2 == 0:
        cnt += AA.count(i)/2
        nokori += 0
    else:
        cnt += AA.count(i)/2
        nokori += 1
print cnt+(len(AA)-2*cnt)/4