P,L,I=0,0,{}
for _ in [0]*int(input()):
    for k in map(int,input().split()):
        if k not in I:I[k]=0
        I[k]+=1
for k in I:
    while I[k]>1:
        P+=1
        I[k]-=2
    L+=I[k]
print(P+L//4)