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n=int(input())
a=map(int,raw_input().split())
l=[0]*200005
for i in a:
    l[i]+=1
c=0
a.sort()
for i in a:
    if l[i] and l[2*i]:
        m=min(l[i],l[2*i])
        l[i]-=m
        l[2 * i]-=m
        c+=m
print c
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