from collections import deque
N=int(input())
P=[0]+list(map(int,input().split()))
G=[set() for _ in range(N+1)]
for i,p in enumerate(P):
    if p!=0:G[p].add(i)
ans=0
for i,g in enumerate(G[1:],1):
    if P[i]!=0:continue
    for nxt in g:
        Q=deque([({i,nxt},nxt)])
        while Q:
            grp,nxt=Q.popleft()
            if len(G[nxt])==0:
                if len(grp)>=3:ans+=1
                continue
            for nxt2 in G[nxt]:
                if nxt2 not in grp:
                    Q.append((grp|{nxt2},nxt2))

print(ans)