n=int(input())
l=[]
for i in range(n):
    s=list(map(int,input().split()))
    l.append(s)
nl=sum(l,[])
c=0
#print(nl)
for i in range(1,11):
    if nl.count(i)>1:
        a=nl.count(i)%2
        b=nl.count(i)//2
        c+=b
        nl=[x for x in nl if x != i]
        if a>0:
            nl.append(i)
c+=len(nl)//4
print(c)