#include <bits/stdc++.h>
using namespace std;
typedef long long ll;       typedef long double ld;  typedef pair<int,int> pii; typedef pair<ll,ll> pll;  typedef vector<int> vi;   typedef vector<ll> vl;
typedef vector<string> vst; typedef vector<bool> vb; typedef vector<ld> vld;    typedef vector<pii> vpii; typedef vector<pll> vpll; typedef vector<vector<int> > vvi;
const int INF = (0x7FFFFFFFL); const ll INFF = (0x7FFFFFFFFFFFFFFFL); const string ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const int MOD = 1e9 + 7;       const int MODD = 998244353;            const string alphabet = "abcdefghijklmnopqrstuvwxyz";
const double PI = acos(-1.0);  const double EPS = 1e-9;               const string Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
int dx[9] = { 1, 0, -1,  0,  1, -1, -1, 1, 0 };
int dy[9] = { 0, 1,  0, -1, -1, -1,  1, 1, 0 };
#define ln '\n'
#define scnaf scanf
#define sacnf scanf
#define sancf scanf
#define SS(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t){cin >> t;}template<typename First, typename...Rest> void MACRO_VAR_Scan(First& first, Rest&...rest){cin >> first;MACRO_VAR_Scan(rest...);}
#define SV(type,c,n) vector<type> c(n);for(auto& i:c)cin >> i;
#define SVV(type,c,n,m) vector<vector<type>> c(n,vector<type>(m));for(auto& r:c)for(auto& i:r)cin >> i;
template<class T>ostream &operator<<(ostream &o,const vector<T>&j){o<<"{";for(int i=0;i<(int)j.size();++i)o<<(i>0?", ":"")<<j[i];o<<"}";return o;}
template<class T,class U>ostream &operator<<(ostream &o,const pair<T,U>&j){o<<"{"<<j.first<<", "<<j.second<<"}";return o;}
template<class T,class U>ostream &operator<<(ostream &o,const map<T,U>&j){o<<"{";for(auto t=j.begin();t!=j.end();++t)o<<(t!=j.begin()?", ":"")<<*t;o<<"}";return o;}
template<class T>ostream &operator<<(ostream &o,const set<T>&j){o<<"{";for(auto t=j.begin();t!=j.end();++t)o<<(t!=j.begin()?", ":"")<<*t;o<<"}";return o;}
inline void print(void){cout << endl;}
template<class Head> void print(Head&& head){cout << head;print();} template<class Head,class... Tail> void print(Head&& head,Tail&&... tail){cout<<head<<" ";print(forward<Tail>(tail)...);}
inline void debug(void){cerr << endl;}
template<class Head> void debug(Head&& head){cerr << head;debug();} template<class Head,class... Tail> void debug(Head&& head,Tail&&... tail){cerr<<head<<" ";debug(forward<Tail>(tail)...);}
template<typename T> void PA(T &a){int ASIZE=sizeof(a)/sizeof(a[0]);for(int ii=0;ii<ASIZE;++ii){cout<<a[ii]<<" \n"[ii==ASIZE-1];}}
template<typename T> void PV(T &v){int VSIZE=v.size();for(int ii=0;ii<VSIZE;++ii){cout<<v[ii]<<" \n"[ii==VSIZE-1];}}
#define ER(x)  cerr << #x << " = " << (x) << endl;
#define ERV(v) {cerr << #v << " : ";for(const auto& xxx : v){cerr << xxx << " ";}cerr << "\n";}
inline void YES(bool x){cout<<((x)?"YES":"NO")<<endl;} inline void Yes(bool x){cout<<((x)?"Yes":"No")<<endl;}  inline void yes(bool x){cout<<((x)?"yes":"no")<<endl;}
inline void yES(bool x){cout<<((x)?"yES":"nO")<<endl;} inline void Yay(bool x){cout<<((x)?"Yay!":":(")<<endl;}
template<typename A,typename B> void sankou(bool x,A a,B b){cout<<((x)?(a):(b))<<endl;}
#define _overload3(_1,_2,_3,name,...) name
#define _REP(i,n) REPI(i,0,n)
#define REPI(i,a,b) for(ll i=ll(a);i<ll(b);++i)
#define REP(...) _overload3(__VA_ARGS__,REPI,_REP,)(__VA_ARGS__)
#define _RREP(i,n) RREPI(i,n,0)
#define RREPI(i,a,b) for(ll i=ll(a);i>=ll(b);--i)
#define RREP(...) _overload3(__VA_ARGS__,RREPI,_RREP,)(__VA_ARGS__)
#define EACH(e,v) for(auto& e : v)
#define PERM(v) sort((v).begin(),(v).end());for(bool c##p=1;c##p;c##p=next_permutation((v).begin(),(v).end()))
#define ADD(a,b) a=(a+ll(b))%MOD
#define MUL(a,b) a=(a*ll(b))%MOD
inline ll MOP(ll x,ll n,ll m=MOD){ll r=1;while(n>0){if(n&1)(r*=x)%=m;(x*=x)%=m;n>>=1;}return r;}
inline ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}inline ll lcm(ll a,ll b){return a*b/gcd(a,b);}inline ll POW(ll a,ll b){ll c=1ll;do{if(b&1)c*=1ll*a;a*=1ll*a;}while(b>>=1);return c;}
template<typename T> inline bool between(T x,T a,T b) {return ((a<=x)&&(x<b));}template<class T> inline T sqr(T x){return x*x;}
template<typename A,typename B> inline bool chmax(A &a,const B &b){if(a<b){a=b;return 1;}return 0;}
template<typename A,typename B> inline bool chmin(A &a,const B &b){if(a>b){a=b;return 1;}return 0;}
#define tmax(x,y,z) max((x),max((y),(z)))
#define tmin(x,y,z) min((x),min((y),(z)))
#define PB push_back
#define MP make_pair
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define SORT(v) sort((v).begin(),(v).end())
#define RSORT(v) sort((v).rbegin(),(v).rend())
#define EXIST(s,e) (find((s).begin(),(s).end(),(e))!=(s).end())
#define EXISTST(s,c) (((s).find(c))!=string::npos)
#define POSL(x,val) (lower_bound(x.begin(),x.end(),val)-x.begin())
#define POSU(x,val) (upper_bound(x.begin(),x.end(),val)-x.begin())
#define SZV(a) int((a).size())
#define SZA(a) sizeof(a)/sizeof(a[0])
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
#define MEMINF(a) memset(a,0x3f,sizeof(a))
#define FILL(a,b) memset(a,b,sizeof(a))
#define UNIQUE(v) sort((v).begin(),(v).end());(v).erase(unique((v).begin(),(v).end()),(v).end())
struct abracadabra{
    abracadabra(){
        cin.tie(0); ios::sync_with_stdio(0);
        cout << fixed << setprecision(20);
    };
} ABRACADABRA;
//#define int long long

//---------------8<---------------8<---------------8<---------------8<---------------//
/*
・グラフ
  > Dijkstra
  > BellmanFord
  > WarshallFloyd
[使用例]
Graph<int> g(N);    // 頂点数N, 重さの型がintのグラフを宣言
add_edge(g,a,b,c);  // グラフgに, aからbへの重さcの無向辺を追加
add_arc(g,a,b,c);   // グラフgに, aからbへの重さcの有向辺を追加
*/

template<typename T> struct Edge {
  int from, to;
  T weight;
  Edge() : from(0), to(0), weight(0) {}
  Edge(int f, int t, T w) : from(f), to(t), weight(w) {}
};
template<typename T> using Edges = vector< Edge< T > >;
template<typename T> using Graph = vector< Edges< T > >;
template<typename T> void add_edge(Graph< T > &g, int from, int to, T w = 1) { g[from].emplace_back(from,to,w); g[to].emplace_back(to,from,w); }
template<typename T> void  add_arc(Graph< T > &g, int from, int to, T w = 1) { g[from].emplace_back(from,to,w); }

/*
・ダイクストラ法
  > O(ElogV) [E:辺の数, V:頂点の数]
[備考] 負辺の存在しないグラフに対する単一始点全点間最短路を求めるアルゴリズム
[使用例]
auto dij = Dijkstra(g,s);     // グラフgにおける, 始点sからの最短路
*/

template<typename T> vector< T > Dijkstra(Graph<T> &g, int from) {
  const auto INF = numeric_limits< T >::max();
  vector< T > dist(g.size(), INF);
  dist[from] = 0;
  using Pi = pair< T, int >;
  priority_queue< Pi, vector< Pi >, greater< Pi > > que;
  que.emplace(dist[from], from);
  while ( !que.empty() ) {
    T weight; int idx;
    tie(weight, idx) = que.top(); que.pop();
    if (dist[idx] < weight) continue;
    for (auto &e : g[idx]) {
      auto next_weight = weight + e.weight;
      if (dist[e.to] <= next_weight) continue;
      dist[e.to] = next_weight;
      que.emplace(dist[e.to], e.to);
    }
  }
  return dist;
}

signed main() {

  SS(int,N);

  Graph<int> g(N);

  REP(i,N) {
    SS(int,A);
    add_arc(g,i,A-1,1);
  }

  auto dij = Dijkstra(g,0);

  if (dij[1] >= INF/10) {
    print(-1);
  } else {
    print(dij[1]);
  }

}


Measured memory_bytes: 6144