#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = a; i < b; i++)
using ll = long long;

int main(){
	int n;
	cin >> n;
	vector<int> p(n), in(n), v(n);
	rep(i, 0, n) {
		cin >> p[i];
		p[i]--;
	}
	vector<vector<int>> g(n);
	rep(i, 0, n) {
		if(p[i] < 0) continue;
		g[i].push_back(p[i]);
		in[p[i]]++;
	}
	using P = pair<int, int>;
	queue<P> q;
	rep(i, 0, n) {
		if(in[i]) continue;
		q.push({i, 0});
	}
	while(q.size()) {
		int u, d;
		tie(u, d) = q.front();
		q.pop();
		if(d == 2) {
			v[u]++;
			continue;
		}
		for(int e : g[u]) {
			q.push({e, d + 1});
		}
	}
	int ans = 0;
	rep(i, 0, n) if(v[i]) ans++;
	cout << ans << endl;
}