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

f = [0] * N
for i in range(N):
    if P[i] == -1:
        continue
    f[P[i]] = 1

ans = 0
st = set()
for i in range(N):
    if f[i] == 1:
        continue

    v = i
    c = 1
    for _ in range(2):
        if P[v] == -1:
            c = 0
        else:
            v = P[v]
    
    if c:
        st.add(i)

print(len(st))