#include <algorithm>
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define ll long long
#define ld long double
#define INF 1000000000000000000
typedef pair<ll, ll> pll;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int N;
    cin >> N;
    vector<ll> A(N);
    rep(i, N) { cin >> A[i]; }

    vector<ll> lmin(N), rmin(N);
    ll lmi = INF, rmi = INF;
    rep(i, N) {
        lmi = min(lmi, A[i]);
        lmin[i] = lmi;
    }

    for (int i = N - 1; i > -1; i--) {
        rmi = min(rmi, A[i]);
        rmin[i] = rmi;
    }

    vector<set<ll>> lse(N), rse(N);
    set<ll> sel, ser;
    sel.insert(INF), ser.insert(INF);
    rep(i, N) {
        sel.insert(A[i]);
        lse[i] = sel;
    }

    for (int i = N - 1; i > -1; i--) {
        ser.insert(A[i]);
        rse[i] = ser;
    }

    ll atype = INF, btype = INF;
    for (int i = 1; i < N - 1; i++) {
        if (A[i] > rmin[i + 1] && A[i] > lmin[i - 1])
            atype = min(atype, A[i] + rmin[i + 1] + lmin[i - 1]);
    }

    for (int i = 1; i < N - 1; i++) {
        ll a = *lse[i - 1].upper_bound(A[i]);
        ll b = *rse[i + 1].upper_bound(A[i]);
        btype = min(btype, a + A[i] + b);
    }

    ll ans = min(atype, btype);
    cout << (ans == INF ? -1 : ans) << endl;
}