#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define rep(i,n) for(ll i=0;i<(n);i++)
#define pll pair<ll,ll>
#define pq priority_queue
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance(c.begin(),lower_bound(all(c),x))
#define ub(c,x) distance(c.begin(),upper_bound(all(c),x))

using namespace std;

template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

const ll INF=1e18;

int main(){
    ll n;
    cin >> n;
    vector<ll> a(n);
    set<ll> le,ri;
    rep(i,n){
        cin >> a[i];
        ri.insert(a[i]);
    }
    ll ans=INF;
    rep(i,n){
        if(i==0){
            le.insert(a[i]);
            ri.erase(a[i]);
        }
        if(i==n-1) break;
        ri.erase(a[i]);
        if(*le.rbegin()>a[i] && *ri.rbegin()>a[i]){
            auto v1=le.upper_bound(a[i]);
            auto v2=ri.upper_bound(a[i]);
            ans=min(ans,*v1+*v2+a[i]);
        }
        if(*le.begin()<a[i] && *ri.begin()<a[i]){
            ans=min(ans,*le.begin()+*ri.begin()+a[i]);
        }
        le.insert(a[i]);
    }
    if(ans==INF) cout << -1 << endl;
    else cout << ans << endl;
}