n=int(input())
p=[0]+list(map(int,input().split()))
d=[0]*(n+1)
for i in range(1,n+1):
  d[p[i]]+=1
v=[0]*(n+1)
q=[i for i in range(1,n+1) if d[i]==0]
for s in q:
  v[s]=1
for s in q:
  t=p[s]
  if t!=0 and v[t]==0:
    v[t]=v[s]+1
    q+=[t]
print(v.count(3))