#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using vin=vector<int>;
using vll=vector<long long>;
using vvin=vector<vector<int>>;
using vvll=vector<vector<long long>>;
using vstr=vector<string>;
using vvstr=vector<vector<string>>;
using vch=vector<char>;
using vvch=vector<vector<char>>;
using vbo=vector<bool>;
using vvbo=vector<vector<bool>>;
using vpii=vector<pair<int,int>>;
using pqsin=priority_queue<int,vector<int>,greater<int>>;
#define mp make_pair
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep2(i,s,n) for(int i=(s);i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define decp(n) cout<<fixed<<setprecision((int)n)
const int inf=1e9+7;
const ll INF=1e18;

int main(){
    int n;cin>>n;
    set<int> l,r;
    vin a(n);
    rep(i,n){
        cin>>a[i];
        r.insert(a[i]);
    }
    r.erase(a[0]);
    vin ls(n),rs(n);
    ls[0]=a[0];rs[0]=a[n-1];
    rep(i,n-1){
        ls[i+1]=min(ls[i],a[i+1]);
        rs[i+1]=min(rs[i],a[n-2-i]);
    }
    int ans=inf;
    rep2(i,1,n-1){
        l.insert(a[i-1]);
        r.erase(a[i]);
        if(a[i]>ls[i-1]&&a[i]>rs[n-2-i])ans=min(ans,ls[i-1]+a[i]+rs[n-2-i]);
        if(l.lower_bound(a[i])==l.end())continue;
        if(r.lower_bound(a[i])==r.end())continue;
        ans=min(ans,a[i]+*l.lower_bound(a[i])+*r.lower_bound(a[i]));
    }
    if(ans==inf)ans=-1;
    cout<<ans<<endl;
}