#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i,n) cin >> a[i];
    vector<int> minr(n),maxr(n);
    vector<int> minl(n),maxl(n);
    int mn = INF,mx = -1;
    rep(i,n){
        minr[i] = mn;
        maxr[i] = mx;
        mn = min(mn,a[i]);
        mx = max(mx,a[i]);
    }
    mn = INF,mx = -1;
    for(int i=n-1;i>=0;i--){
        minl[i] = mn;
        maxl[i] = mx;
        mn = min(mn,a[i]);
        mx = max(mx,a[i]);
    }
    ll ans = LINF;
    for(int i=1;i<n-1;i++){
        ll res = a[i];
        if(minr[i] < a[i] && minl[i] < a[i]){
            ans = min(ans,res + minr[i] + minl[i]);
        }
        if(maxr[i] > a[i] && maxl[i] > a[i]){
            ans = min(ans,res + maxr[i] + maxl[i]);
        }
    }
    if(ans==LINF) cout << -1 << endl;
    else cout << ans << endl;
    return 0;
}