from collections import defaultdict
N = int(input())
P = list(map(int, input().split()))

shikigami = defaultdict(lambda: -1)
ans = 0
for i in range(N):
    p = P[i]-1
    if p == -1:
        cnt = 0
        c = i
        while shikigami[c] != -1:
            cnt += 1
            c = shikigami[c]
        ans += cnt >= 2
    shikigami[p] = i

print(ans)