from collections import deque
N = int(input())
P = [int(x) - 1 for x in input().split()]

deg = [0] * N
f = [0] * N
g = [[] for i in range(N)]
for i in range(N):
    if P[i] == -1: continue
    deg[P[i]] += 1
    g[i].append(P[i])
    f[i] = 1

dq = deque()
dp = [-1] * N
for i in range(N):
    if deg[i] == 0:
        dq.append(i)
        dp[i] = 0

while dq:
    now = dq.popleft()
    
    for nxt in g[now]:
        deg[nxt] -= 1
        dp[nxt] = max(dp[nxt], dp[now] + 1)
        if deg[nxt] == 0:
            dq.append(nxt)
# print(dp, deg, f)

print(sum([f[i] == 0 and dp[i] >= 2 for i in range(N)]))