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

g = [list() for i in range(N)]
g_rev = [list() for i in range(N)]
for i in range(N):
    if P[i] != 0:
        g[P[i] - 1].append(i)
        g_rev[i].append(P[i]-1)

depth = [-1] * N


ans = 0


def dfs(v, d=0, pre=-1):
    depth[v] = d

    for u in g[v]:
        if u == pre:
            continue
        dfs(u, d + 1, pre=v)


for i in range(N):
    if P[i] == 0:
        dfs(i)

is_ss = [False] * N

ans = 0
for i in range(N):
    if depth[i] >= 2:
        j = P[P[i] - 1]-1
        is_ss[j] = True
ans = sum(is_ss)
print(ans)