90pts

#include<bits/stdc++.h>
#define ll long long
using namespace std;
set<ll> a;
ll n;
int main(){
    cin>>n;
    while(n--){
        ll t;
        cin>>t;
        a.insert(t);
    }
    if(a.size()<2){
        cout<<-1;
        return 0;
    }
    set<ll>::iterator it=a.begin();
    for(int i=1;i<=a.size()-2;i++,it++){
        if(i==a.size()-2){
            cout<<*it;
            return 0;
        }
    }
}