#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <set>
#include <array>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

template <class T>
struct SegmentTree {
    SegmentTree(int n) : n(n) {
        for (m = 2; m < n; m *= 2);
        t = vector<T>(m + n + n % 2);
    }
    T &operator[](int i) {
        return t[m + i];
    }
    const T &root() const {
        return t[1];
    }
    void build() {
        for (int i = (n - 1 + m) / 2; i > 0; i--) t[i] = t[i * 2] * t[i * 2 + 1];
    }
    void update(int i, const T &o) {
        for (t[i += m] = o; i /= 2, i > 0;) t[i] = t[i * 2] * t[i * 2 + 1];
    }
    T query(int l, int r) {
        T o0, o1;
        for (l += m, r += m; l < r; l /= 2, r /= 2) {
            if (l & 1) o0 = o0 * t[l++];
            if (r & 1) o1 = t[--r] * o1;
        }
        return o0 * o1;
    }
    vector<T> t;
    int n, m;
};
struct MaxMin {
    constexpr MaxMin() : ma(0), mi(1 << 30) {}
    MaxMin(int ma, int mi) : ma(ma), mi(mi) {}
    MaxMin operator*(const MaxMin &o) const {
        return { max(ma, o.ma), min(mi, o.mi) };
    }
    int ma, mi;
};

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

    int n;
    cin >> n;

    SegmentTree<MaxMin> st(n);

    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        st[i] = { a[i], a[i] };
    }
    st.build();

    vector<array<int, 2>> p(n, { -1, -1 });
    for (int h = 0; h < 2; h++) {
        set<int> st0;
        for (int i = 0; i < n; i++) {
            int j = h == 0 ? i : n - 1 - i;
            auto [it, b] = st0.insert(a[j]);
            it++;
            if (it != st0.end()) {
                p[j][h] = *it;
            }
        }
    }

    int r = 1 << 30;
    for (int i = 0; i < n; i++) {
        auto [ma0, mi0] = st.query(0, i);
        auto [ma1, mi1] = st.query(i + 1, n);
        if (a[i] > mi0 && a[i] > mi1) r = min(r, mi0 + a[i] + mi1);
        if (p[i][0] >= 0 && p[i][1] >= 0) {
            r = min(r, p[i][0] + a[i] + p[i][1]);
        }
    }

    cout << (r == 1 << 30 ? -1 : r) << endl;

    return 0;
}