#include <limits>
#include <initializer_list>
#include <utility>
#include <bitset>
#include <tuple>
#include <type_traits>
#include <functional>
#include <string>
#include <array>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <iterator>
#include <algorithm>
#include <complex>
#include <random>
#include <numeric>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <regex>
#include <cassert>
#include <cstddef>
#ifdef CPP17
#include <variant>
#endif

#define endl codeforces

#define ALL(v) std::begin(v), std::end(v)
#define ALLR(v) std::rbegin(v), std::rend(v)

using ll = std::int64_t;
using ull = std::uint64_t;
using pii = std::pair<int, int>;
using tii = std::tuple<int, int, int>;
using pll = std::pair<ll, ll>;
using tll = std::tuple<ll, ll, ll>;
using size_type = ssize_t;
template <typename T> using vec = std::vector<T>;
template <typename T> using vvec = vec<vec<T>>;

template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }

template <typename T, std::size_t Head, std::size_t... Tail> 
struct multi_dim_array { using type = std::array<typename multi_dim_array<T, Tail...>::type, Head>; };

template <typename T, std::size_t Head> 
struct multi_dim_array<T, Head> { using type = std::array<T, Head>; };

template <typename T, std::size_t... Args> using mdarray = typename multi_dim_array<T, Args...>::type;

#ifdef CPP17
template <typename T, typename F, typename... Args> 
void fill_seq(T &t, F f, Args... args) { 
    if constexpr (std::is_invocable<F, Args...>::value) { 
        t = f(args...); 
    } else { 
        for (size_type i = 0; i < t.size(); i++) fill_seq(t[i], f, args..., i); 
    } 
}
#endif

template <typename T> vec<T> make_v(size_type sz) { return vec<T>(sz); }

template <typename T, typename... Tail> 
auto make_v(size_type hs, Tail&&... ts) { 
    auto v = std::move(make_v<T>(std::forward<Tail>(ts)...)); 
    return vec<decltype(v)>(hs, v); 
}

namespace init__ { 
struct InitIO { 
    InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } 
} init_io; 
}

ssize_t ceil_pow2(ssize_t s) {
    ssize_t ret = 1;
    while (ret < s) ret *= 2;
    return ret;
}

namespace segtree {

template <typename T, typename Op>
struct SegmentTree {
    vec<T> nodes;
    Op op;
    T id_ele;

    auto get_children_idx(ssize_t idx) const -> std::pair<ssize_t, ssize_t> {
        return std::make_pair(2 * idx + 1, 2 * idx + 2);
    }

    T get_merged(ssize_t idx) const {
        ssize_t a, b;
        std::tie(a, b) = get_children_idx(idx);
        return op(nodes[a], nodes[b]);
    }

public:
    SegmentTree(const vec<T> &init_v, Op op, T id_ele)
        : op(op), id_ele(id_ele)
    {
        build(init_v);
    }

    void build(const vec<T> &v) {
        nodes.resize(ceil_pow2(v.size()) * 2 - 1, id_ele);
        ssize_t sz = size();
        std::copy(ALL(v), nodes.begin() + sz - 1);
        build_parents();
    }

    void build_parents() {
        ssize_t sz = size();
        for (ssize_t i = sz - 2; 0 <= i; i--) nodes[i] = get_merged(i);
    }

    ssize_t size() const {
        return (nodes.size() + 1) / 2;
    }

    const T& operator [](ll idx) const {
        return nodes[idx + size() - 1];
    }

    T get_query(ll ql, ll qr) const {
        return get_query(ql, qr, id_ele);
    }

    T get_query(ll ql, ll qr, T init) const {
        T ret = init;
        ssize_t lnode = ql + size(), rnode = qr + size();
        while (lnode < rnode) {
            if (lnode & 1) {
                ret = std::move(op(nodes[lnode - 1], ret));
                lnode++;
            }
            if (rnode & 1) {
                rnode--;
                ret = std::move(op(ret, nodes[rnode - 1]));
            }
            lnode /= 2;
            rnode /= 2;
        }
        return ret;
    }

    void update_query(ll idx, T val) {
        idx += size() - 1;
        nodes[idx] = val;
        while (idx) {
            ll pidx = (idx - 1) / 2;
            nodes[pidx] = get_merged(pidx);
            idx = pidx;
        }
    }

    template <typename F>
    ssize_t lower_bound(F f) const {
        T sum = id_ele;
        ssize_t l = 0, r = size(), idx = 0, bidx = 0;
        if (!f(nodes[0])) return -1;
        while (true) {
            if (r - l == 1) {
                if (!f(sum)) bidx++;
                break;
            }
            auto lidx = 2 * idx + 1;
            auto ridx = lidx + 1;
            T nsum = op(sum, nodes[lidx]);
            ssize_t m = (l + r) / 2;
            if (f(nsum)) {
                r = m;
                idx = lidx;
            } else {
                l = m;
                idx = ridx;
                bidx = m;
                sum = std::move(nsum);
            }
        }
        return bidx;
    }
};

}

int main() {
    const ll inf = 5e15;
    ll n;
    std::cin >> n;
    vec<ll> av(n);
    for (ll &e : av) std::cin >> e;
    vec<ll> ord(n);
    std::iota(ALL(ord), 0ll);

    ll ans = inf;

    {
        auto merge = [&](ll a, ll b) { return std::min(a, b); };
        std::sort(ALL(ord), [&](ll a, ll b) { return av[a] < av[b]; });
        vec<ll> init_v(n, inf);
        segtree::SegmentTree<ll, decltype(merge)> seg(init_v, merge, inf);
        for (ll i : ord) {
            ll a = av[i];
            if (i != 0 && i != n - 1) {
                ll lv = seg.get_query(0, i);
                ll rv = seg.get_query(i + 1, n);
                chmin(ans, lv + rv + a);
            }
            seg.update_query(i, a);
        }
    }
    {
        auto merge = [&](ll a, ll b) { return std::min(a, b); };
        std::reverse(ALL(ord));
        vec<ll> init_v(n, inf);
        segtree::SegmentTree<ll, decltype(merge)> seg(init_v, merge, inf);
        for (ll i : ord) {
            ll a = av[i];
            if (i != 0 && i != n - 1) {
                ll lv = seg.get_query(0, i);
                ll rv = seg.get_query(i + 1, n);
                chmin(ans, lv + rv + a);
            }
            seg.update_query(i, a);
        }
    }

    std::cout << (ans == inf ? -1 : ans) << "\n";
    return 0;
}