#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i ++)
using namespace std;
using ll = long long;
using PL = pair<ll,ll>;
using P = pair<int,int>;
constexpr int INF = 1000000000;
constexpr long long HINF = 1000000000000000;
constexpr long long MOD = 1000000007;
constexpr double EPS = 1e-10;
constexpr double PI = 3.14159265358979;

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

    vector<int> left_min(N + 1),left_max(N + 1),right_min(N + 1),right_max(N + 1);
    left_min[0] = INF; left_max[0] = 0; right_min[N] = INF; right_max[N] = 0;
    rep(i,N) {
        left_min[i + 1] = min(left_min[i],A[i]);
        left_max[i + 1] = max(left_max[i],A[i]);
    }
    for (int i = N - 1;i >= 0;--i) {
        right_min[i] = min(right_min[i + 1],A[i]);
        right_max[i] = max(right_max[i + 1],A[i]);
    }
    int ans = INF;
    rep(i,N) {
        if (0 < i < N - 1 && left_min[i] > A[i] && A[i] < right_min[i + 1]) ans = min(ans,A[i] + left_min[i] + right_min[i + 1]);
        if (0 < i < N - 1 && left_min[i] < A[i] && A[i] > right_min[i + 1]) ans = min(ans,A[i] + left_min[i] + right_min[i + 1]);
    }
    if (ans == INF) cout << -1 << endl;
    else cout << ans << endl;
    return 0;
}