#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<ll> lse(N), rse(N);
    set<ll> sel, ser;
    sel.insert(INF), ser.insert(INF);
    rep(i, N) {
        sel.insert(A[i]);
        if (i - 1 >= 0)
            lse[i] = *sel.upper_bound(A[i]);
    }

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

    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++) {
        btype = min(btype, A[i] + lse[i] + rse[i]);
    }

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