#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
namespace my{
#define eb emplace_back
#define LL(...) ll __VA_ARGS__;lin(__VA_ARGS__)
#define VL(n,...) vec<ll>__VA_ARGS__;setsize({n},__VA_ARGS__);lin(__VA_ARGS__)
#define FO(n) for(ll ij=n;ij-->0;)
#define FOR(i,...) for(auto[i,i##stop,i##step]=range(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define fo(i,...) FO##__VA_OPT__(R)(i __VA_OPT__(,__VA_ARGS__))
#define fe(a,i,...) for(auto&&__VA_OPT__([)i __VA_OPT__(,__VA_ARGS__]):a)
#define single_testcase void solve();}int main(){my::io();my::solve();}namespace my{
void io(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);}
using ll=long long;
constexpr auto range(bool s,auto...a){array<ll,3>r{0,0,1};ll I=0;((r[I++]=a),...);if(!s&&I==1)swap(r[0],r[1]);r[0]-=s;if(s)r[2]*=-1;return r;}
constexpr char newline=10;
constexpr char space=32;
constexpr auto schrodinger(bool p,char c){return string(p,c);}
constexpr auto even(auto x){return~x&1;}

template<class F=less<>>auto&sort(auto&a,F f={}){ranges::sort(a,f);return a;}
auto&unique(auto&a){sort(a).erase(ranges::unique(a).begin(),a.end());return a;}

template<ll k>auto pack_kth(const auto&...a){return get<k>(make_tuple(a...));}
template<class T,ll n>auto pack_slice(const auto&...a){return[&]<size_t...I>(index_sequence<I...>){return array<T,n>{get<I>(forward_as_tuple(a...))...};}(make_index_sequence<n>{});}

template<class V>concept vectorial=is_base_of_v<vector<typename V::value_type>,V>;
template<class T>struct vec_attr{using core_type=T;static constexpr int rank=0;};
template<vectorial V>struct vec_attr<V>{using core_type=typename vec_attr<typename V::value_type>::core_type;static constexpr int rank=vec_attr<typename V::value_type>::rank+1;};
template<class T>using core_t=vec_attr<T>::core_type;
template<class V>istream&operator>>(istream&i,vector<V>&v){fe(v,e)i>>e;return i;}
template<class V>ostream&operator<<(ostream&o,const vector<V>&v){fe(v,e)o<<e<<schrodinger(&e!=&v.back(),vectorial<V>?newline:space);return o;}

template<class V>struct vec;
template<int rank,class T>struct tensor_helper{using type=vec<typename tensor_helper<rank-1,T>::type>;};
template<class T>struct tensor_helper<0,T>{using type=T;};
template<int rank,class T>using tensor=typename tensor_helper<rank,T>::type;

template<class V>struct vec:vector<V>{
  using vector<V>::vector;
  vec(const vector<V>&v){vector<V>::operator=(v);}

  template<class...A>requires(sizeof...(A)>=3)vec(A...a){const ll n=sizeof...(a)-1;auto t=pack_slice<ll,n>(a...);ll s[n];fo(i,n)s[i]=t[i];*this=make_vec(s,pack_kth<n>(a...));}
  template<class T,ll n,ll i=0>static auto make_vec(const ll(&s)[n],T x){if constexpr(i==n-1)return vec<T>(s[i],x);else{auto X=make_vec<T,n,i+1>(s,x);return vec<decltype(X)>(s[i],X);}}

  vec&operator^=(const vec&u){this->insert(this->end(),u.begin(),u.end());return*this;}
  vec operator^(const vec&u)const{return vec{*this}^=u;}
  vec&operator+=(const vec&u){vec&v=*this;assert(v.size()==u.size());fo(i,v.size())v[i]+=u[i];return v;}
  vec&operator-=(const vec&u){vec&v=*this;assert(v.size()==u.size());fo(i,v.size())v[i]-=u[i];return v;}
  vec operator+(const vec&u)const{return vec{*this}+=u;}
  vec operator-(const vec&u)const{return vec{*this}-=u;}
  vec&operator++(){fe(*this,e)++e;return*this;}
  vec&operator--(){fe(*this,e)--e;return*this;}
  vec operator-()const{vec v=*this;fe(v,e)e=-e;return v;}

  vec&operator%=(auto M){vec&v=*this;fe(v,e)e%=M;return v;}
  vec operator%(auto M)const{return vec{*this}%=M;}

  ll size()const{return vector<V>::size();}

  auto pop_front(){auto r=*this->begin();this->erase(this->begin());return r;}

  template<class F=less<>>auto sort(F f={})const{vec v=*this;ranges::sort(v,f);return v;}

  auto unique()const{auto r=sort();r.erase(ranges::unique(r).begin(),r.end());return r;}
};
template<class...A>requires(sizeof...(A)>=2)vec(A...a)->vec<tensor<sizeof...(a)-2,remove_reference_t<decltype(get<sizeof...(a)-1>(declval<tuple<A...>>()))>>>;
vec(ll)->vec<ll>;

template<ll n,class...A>void setsize(const ll(&l)[n],A&...a){((a=vec<void*>::make_vec(l,core_t<A>{})),...);}

void lin(auto&...a){(cin>>...>>a);}
void pp(auto&&...a){ll n=sizeof...(a);((cout<<a<<schrodinger(--n>0,space)),...);cout<<newline;}

void sort(auto&...a){vec<common_type_t<decltype(a)...>>v;(v.eb(a),...);sort(v);ll I=0;((a=v[I++]),...);}

struct dsu{
  ll n;
  vec<int>par_or_size;

  dsu(ll n):n(n),par_or_size(n,-1){}

  auto merge(ll a,ll b){
    ll x=leader(a),y=leader(b);
    if(x==y)return tuple{x,a,y,b};
    if(-par_or_size[x]<-par_or_size[y])swap(x,y),swap(a,b);

    par_or_size[x]+=par_or_size[y];
    par_or_size[y]=x;
    return tuple{x,a,y,b};
  }

  ll leader(ll a){
    assert(0<=a&&a<n);
    if(par_or_size[a]<0)return a;
    return par_or_size[a]=leader(par_or_size[a]);
  }

  ll size(ll a){return-par_or_size[leader(a)];}

  auto groups(){
    vec<ll>leader_buf(n),group_size(n);
    fo(u,n){
      leader_buf[u]=leader(u);
      group_size[leader_buf[u]]++;
    }
    vec<vec<ll>>res(n);
    fo(u,n)res[u].reserve(group_size[u]);
    fo(u,n)res[leader_buf[u]].eb(u);

    fe(res,e)sort(e);
    unique(res);
    if(res[0].empty())res.pop_front();
    return res;
  }
};

single_testcase
void solve(){
  LL(N);
  VL(N,p);--p;
  atcoder::dsu uf(N);
  fo(i,N)uf.merge(i,p[i]);

  ll s=0;
  auto gs=uf.groups();
  fe(gs,g)s+=g.size()-1;
  pp(even(s)?1:-1);
}}