#yuki_029

n=int(raw_input())
t=[]
for i in xrange(n):
 s=map(int,raw_input().split())
 t+=s
u=[0 for i in xrange(11)]
for i in xrange(1,11):
 u[i]= t.count(i)
res1=0
res2=0
for i in xrange(1,11):
 res1+=u[i]/2
 res2+=u[i]%2
res=res1+res2/4
print res