from collections import deque
N=int(input())
P=list(map(int,input().split()))
G=[[]for _ in range(N+1)]
S=[1 for _ in range(N+1)]
for i,p in enumerate(P,1):
    G[i].append(p)
    S[p]=0
ans=0
for i in range(1,N+1):
    if S[i]==0:continue
    Q=deque([(i,0)])
    while Q:
        now,cnt=Q.popleft()
        if cnt==2:
            if len(G[now])==1 and G[now][0]==0:
                ans+=1
            break
        for nxt in G[now]:
            if nxt==0:continue
            Q.append((nxt,cnt+1))
print(ans)