#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
signed main() {
    #ifdef HOME
    freopen("input.txt", "r", stdin);
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif

    int n;
    cin >> n;
    vector <int> a(n);
    for (int i = 0; i < n; ++i) 
        cin >> a[i];

    const int INF = 1e18;
    int ans = INF;

    vector <int> l1(n,INF), l2(n,INF), r1(n,INF), r2(n,INF);
    //1 - less

    set <int> ms;
    for (int i = 0; i < n; ++i) {
        ms.insert(a[i]);
        auto t = ms.find(a[i]);
        if (a[i] != *ms.rbegin()) {
            l2[i] = *next(t);
        }
        if (*ms.begin() < a[i]) {
            l1[i] = *ms.begin();
        }   
    }   
    ms.clear();
    for (int i = n - 1; i >= 0; --i) {
        ms.insert(a[i]);
        auto t = ms.find(a[i]);
        if (a[i] != *ms.rbegin()) {
            r2[i] = *next(t);
        }
        if (*ms.begin() < a[i]) {
            r1[i] = *ms.begin();
        }   
    }   

    for (int i = 0; i < n; ++i) {
        //cout << i << ' ' << l2[i] << ' ' << r2[i] << ' ' << a[i] << endl;
        ans = min(ans, l1[i]+r1[i]+a[i]);
        ans = min(ans, l2[i]+r2[i]+a[i]);
    }   

    if (ans == INF)
        cout << -1 << endl;
    else
        cout << ans << endl;
}