import sys
input = sys.stdin.readline

N=int(input())
A=list(map(int,input().split()))

ANS=set()

for i in range(N):
    if A[i]==0:
        continue

    x=A[i]-1
    if A[x]==0:
        continue
    y=A[x]-1

    if A[y]==0:
        ANS.add(y)

print(len(ANS))