#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n;
    cin >> n;
    vector<int> p(n);
    rep(i,n) cin >> p[i];
    int ans = 0;
    vector<int> d(n);
    rep(i,n) {
        p[i]--;
        if(p[i]!=-1) d[p[i]]++;
    }
    set<int> st;
    rep(i,n) {
        if(p[i]!=-1 && p[p[i]]!=-1 && d[i]==0) st.insert(p[p[i]]);
    }
    ans = st.size();
    cout << ans << endl;
    return 0;
}