n = int(input())
d = {}
pup = 0
item = 0
for x in range(1, 11):
    d[x] = 0
for _ in range(n):
    a = [int(x) for x in input().split()]
    for b in a:
        d[b] = d[b] + 1
for k in d.keys():
    if d[k] >=2:
        pup += d[k]//2
    item += (d[k] % 2)
print(pup + item //4)