/*
#include<kyopro/master>
void self::main(){
  LL(N);
  VL(N,a);
  auto cnt=a.count_enumerate(a.max());
  
  ll su=0;
  fo(i,cnt.size()){
    su+=min(cnt[i],2);
    if(cnt[i]>=2)continue;
    if(cnt[i]==1){
      if(su==N)done(i);
      else done(i+1);
    }
    if(cnt[i]==0)done(i);
  }
  pp(cnt.size());
}
*/

#include<bits/stdc++.h>
using namespace std;
namespace self{void main();void sub();template<ostream&o>void pp(const auto&...a);void epp(const auto&...a);}
int main(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);self::main();}
#define done(...) return pp(__VA_ARGS__)
#define RD(T,...) T __VA_ARGS__;lin(__VA_ARGS__)
#define LL(...) RD(ll,__VA_ARGS__)
#define RDVL(T,n,...) vec<T>__VA_ARGS__;fe(refs(__VA_ARGS__),e)e.get().resizes(n);lin(__VA_ARGS__)
#define VL(n,...) RDVL(ll,n,__VA_ARGS__)
#define fo(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define fe(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):a)
namespace self{
using ll=long long;
constexpr auto refs(auto&...a){return array{ref(a)...};}
template<class T>constexpr auto for_range(T s,T b){T a=0;if(s)swap(a,b);return array{a-s,b,1-s*2};}
void lin(auto&...a){(cin>>...>>a);}
auto min(auto...a){return min(initializer_list<common_type_t<decltype(a)...>>{a...});}
template<class A,class B=A>struct pair{
  A a;B b;
  pair()=default;
  pair(A a,B b):a(a),b(b){}
  auto operator<=>(const pair&)const=default;
};
template<class...A>using pack_back_t=tuple_element_t<sizeof...(A)-1,tuple<A...>>;
}
namespace self{
template<class V>concept vectorial=is_base_of_v<vector<typename remove_cvref_t<V>::value_type>,remove_cvref_t<V>>;
template<class V>istream&operator>>(istream&i,vector<V>&v){fe(v,e)i>>e;return i;}
template<class V>constexpr int depth=0;
template<class T>struct core_t_helper{using type=T;};
template<class T>using core_t=core_t_helper<T>::type;
template<class V>struct vec;
template<int D,class T>struct hvec_helper{using type=vec<typename hvec_helper<D-1,T>::type>;};
template<class T>struct hvec_helper<0,T>{using type=T;};
template<int D,class T>using hvec=hvec_helper<D,T>::type;
template<class V>struct vec:vector<V>{
  static constexpr int D=depth<V>+1;
  using C=core_t<V>;
  using vector<V>::vector;
  void resizes(const auto&...a){if constexpr(sizeof...(a)==D)*this=make(a...,C{});else{ }}
  static auto make(ll n,const auto&...a){
    if constexpr(sizeof...(a)==1)return vec<C>(n,array{a...}[0]);
    else { }
  }
  ll size()const{return vector<V>::size();}
  template<class T=C>auto fold(auto&&f)const{
    pair<T,bool>res{};
    fe(*this,e){
      if constexpr(!vectorial<V>){
        if(res.b)f(res.a,e);
        else res={e,1};
      }else { }

    }
    return res;
  }
  auto max()const{return fold([](auto&a,auto b){if(a<b)a=b;}).a;}
  auto min()const{return fold([](auto&a,auto b){if(b<a)a=b;}).a;}
  auto count_enumerate(C M)const{
    assert(min()>=0);
    vec<C>res(M+1);
    auto f=[&]<class U>(auto&f,const vec<U>&v){
      fe(v,e){
        if constexpr(vectorial<U>){ }
        else if(e<=M)res[e]++;
      }
    };
    f(f,*this);
    return res;
  }
};
template<class...A>requires(sizeof...(A)>=2)vec(const A&...a)->vec<hvec<sizeof...(A)-2,pack_back_t<A...>>>;
}
template<ostream&o=cout>void self::pp(const auto&...a){const char*c="";((o<<c<<a,c=" "),...);o<<'\n';}
void self::main(){
  LL(N);
  VL(N,a);
  auto cnt=a.count_enumerate(a.max());

  ll su=0;
  fo(i,cnt.size()){
    su+=min(cnt[i],2);
    if(cnt[i]>=2)continue;
    if(cnt[i]==1){
      if(su==N)done(i);
      else done(i+1);
    }
    if(cnt[i]==0)done(i);
  }
  pp(cnt.size());
}