POW=0
ITEM={}
for _ in [0]*int(input()):
    for x in map(int,input().split()):
        if x not in ITEM:ITEM[x]=0
        ITEM[x]+=1

LEFT=[]
for k,v in ITEM.items():
    while ITEM[k]>1:
        POW+=1
        ITEM[k]-=2
    LEFT.append(ITEM[k])
print(POW+ sum(LEFT)//4)