#include <iostream>
#include <algorithm>
#include <vector>
#include <set>

bool judge(int a, int b, int c) {
    return ((a < b && b > c) || (a > b && b < c));
}

constexpr int INF = 1 << 29;

void solve() {
    int n;
    std::cin >> n;

    std::vector<int> xs(n);
    for (auto& x : xs) std::cin >> x;

    std::vector<int>
        lsmall(n, INF), lbig(n, INF),
        rsmall(n, INF), rbig(n, INF);

    {
        int lmin = INF;
        std::set<int> s;
        for (int i = 0; i < n; ++i) {
            if (lmin < xs[i]) lsmall[i] = lmin;
            auto it = s.upper_bound(xs[i]);
            if (it != s.end()) lbig[i] = *it;

            lmin = std::min(lmin, xs[i]);
            s.insert(xs[i]);
        }
    }

    {
        int rmin = INF;
        std::set<int> s;
        for (int i = n - 1; i >= 0; --i) {
            if (rmin < xs[i]) rsmall[i] = rmin;
            auto it = s.upper_bound(xs[i]);
            if (it != s.end()) rbig[i] = *it;

            rmin = std::min(rmin, xs[i]);
            s.insert(xs[i]);
        }
    }

    int ans = INF;
    for (int i = 0; i < n; ++i) {
        ans = std::min({ans,
                        lsmall[i] + xs[i] + rsmall[i],
                        lbig[i] + xs[i] + rbig[i]});
    }

    std::cout << (ans == INF ? -1 : ans) << "\n";
}

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

    solve();

    return 0;
}