#include <bits/stdc++.h>
#define REP(i, n)     for(int i = 0; i < (int)(n); ++i)
#define RREP(i, n)    for(int i = (int)(n); i-- > 0;)
#define FOR(i, l, r)  for(int i = (int)(l); i < (int)(r); ++i)
#define RFOR(i, l, r) for(int i = (int)(r); i-- > (int)(l);)
#define ALL(v)        std::begin(v), std::end(v)
using llong = long long;
using vi    = std::vector<int>;
using vvi   = std::vector<vi>;
using pii   = std::pair<int, int>;
using namespace std;
constexpr int       INF  = 1e9;
constexpr long long LINF = 1e18;
constexpr double    EPS  = 1e-10;
constexpr int       MOD  = 998'244'353;
constexpr int       MOD2 = 1e9 + 7;

template <typename C, typename Tr, typename R, typename T = std::ranges::range_value_t<R>>
    requires std::ranges::output_range<R, T>
inline auto &operator>>(std::basic_istream<C, Tr> &is, R &r) {
    for(auto &elem : r) is >> elem;
    return is;
}

template <typename C, typename Tr, std::ranges::input_range R>
    requires(!std::convertible_to<R, const char *>)
inline auto &operator<<(std::basic_ostream<C, Tr> &os, const R &r) {
    if(std::ranges::empty(r)) return os;
    auto iter = std::ranges::cbegin(r);
    const auto end = std::ranges::cend(r);
    os << *iter++;
    while(iter != end) os << " " << *iter++;
    return os;
}

#ifdef DEBUG

#include <debug>

#else

#define debug(...) static_cast<void>(0)

#endif

int main(){
    int n;
    cin>>n;

    vi p(n);
    vi deg(n,0);
    for(auto &e:p){
        cin>>e;
        e--;
        if(e!=-1) deg[e]++;
    }
    debug(p);
    debug(deg);

    vector<bool> flag(n,false);
    auto dfs=[&](auto self,int u,int depth)->void{
        if(depth==2){
            flag[u]=true;
            return;
        }
        if(p[u]!=-1) self(self,p[u],depth+1);
    };
    REP(i,n){
        if(deg[i]==0) dfs(dfs,i,0);
    }    

    auto ans=count(ALL(flag),true);
    cout<<ans<<endl;
}