#include <bits/stdc++.h>
using namespace std;
template <class T> inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return 1;
    }
    return 0;
}
void debug() { cerr << "\n"; }
template <class T> void debug(const T &x) { cerr << x << "\n"; }
template <class T, class... Args> void debug(const T &x, const Args &... args) {
    cerr << x << " ";
    debug(args...);
}
template <class T> void debugVector(const vector<T> &v) {
    for(const T &x : v) {
        cerr << x << " ";
    }
    cerr << "\n";
}
using ll = long long;

#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
const double EPS = 1e-7;
const int INF = 1 << 30;
const ll LLINF = 1LL << 60;
const double PI = acos(-1);
constexpr int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

//-------------------------------------

template <typename Monoid> struct SegmentTree {
    using F = function<Monoid(Monoid, Monoid)>;

  private:
    int n;
    vector<Monoid> node;
    Monoid E;
    F f;

  public:
    SegmentTree(vector<Monoid> v, Monoid e, const F func) : f(func), E(e) {
        int sz = v.size();
        n = 1;
        while(n < sz) {
            n *= 2;
        }
        node.resize(2 * n - 1, E);
        for(int i = 0; i < sz; i++) {
            node[i + n - 1] = v[i];
        }
        for(int i = n - 2; i >= 0; i--) {
            node[i] = f(node[2 * i + 1], node[2 * i + 2]);
        }
    }

    void update(int i, Monoid val) {
        i += (n - 1);
        node[i] = val;
        while(i > 0) {
            i = (i - 1) / 2;
            node[i] = f(node[2 * i + 1], node[2 * i + 2]);
        }
    }

    Monoid query(int a, int b, int i = 0, int l = 0, int r = -1) {
        if(r < 0) {
            r = n;
        }
        if(r <= a || b <= l) {
            return E;
        }
        if(a <= l && r <= b) {
            return node[i];
        }
        Monoid vl = query(a, b, 2 * i + 1, l, (l + r) / 2);
        Monoid vr = query(a, b, 2 * i + 2, (l + r) / 2, r);
        return f(vl, vr);
    }

    Monoid operator[](const int &i) const { return node[i + n - 1]; }
};

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    vector<ll> a(n);
    for(auto &it : a) {
        cin >> it;
    }
    SegmentTree<ll> segmin(a, LLINF, [](ll x, ll y) { return min(x, y); });
    ll ans = LLINF;
    // min max minを探す
    for(int i = 0; i < n; i++) {
        ll l = segmin.query(0, i);
        ll r = segmin.query(i + 1, n);
        if(l < a[i] && r < a[i]) {
            chmin(ans, l + a[i] + r);
        }
    }
    // 大小大
    vector<ll> memo = a;
    // 今見てる要素より左にあって、今見てる要素よりも大きいa[i]の集合
    set<ll> se;
    for(int i = 0; i < n; i++) {
        while(!se.empty()) {
            if(*se.begin() >= a[i]) {
                break;
            } else {
                se.erase(se.begin());
            }
        }
        if(se.empty()) {
            memo[i] += LLINF;
        } else {
            memo[i] += *se.begin();
        }
        se.insert(a[i]);
    }
    se.clear();
    for(int i = n - 1; i >= 0; i--) {
        while(!se.empty()) {
            if(*se.begin() > a[i]) {
                break;
            } else {
                se.erase(se.begin());
            }
        }
        if(se.empty()) {
            memo[i] += LLINF;
        } else {
            memo[i] += *se.begin();
        }
        se.insert(a[i]);
    }
    chmin(ans, *min_element(ALL(memo)));
    cout << (ans >= LLINF ? -1 : ans) << endl;
}