n=int(input())
pp=list(map(int,input().split()))
pp=[p-1 for p in pp]

top=[1]*n
for p in pp:
	if p==-1:continue
	top[p]=0

ans=set()
for i in range(n):
	if top[i]:
		j=pp[i]
		if j!=-1 and pp[j]!=-1:ans.add(pp[j])

print(len(ans))