#include <bits/stdc++.h>
using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define DEBUG(...)
#endif

template <class T> struct segtree {
  const int n;
  vector<T> t;
  segtree(int _n = 0) : n(_n), t(2 * n) {}
  T& operator[](int i) { return t[n + i]; }
  void build() { for (int i = n; i--; ) t[i] = t[2 * i] * t[2 * i + 1]; }
  T fold(int l, int r) const {
    T a, b;
    for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
      if (l & 1) a = a * t[l++];
      if (r & 1) b = t[--r] * b;
    }
    return a * b;
  }
  void set(int i, T a) {
    t[i += n] = a;
    while (i >>= 1) t[i] = t[2 * i] * t[2 * i + 1];
  }
};

template <class T> constexpr T inf = numeric_limits<T>::max() / 2.1;

template <class T> struct mini {
  T v = inf<T>;
  mini operator*(mini b) const {
    return b.v < v ? b : *this;
  }
};
template <class T> struct maxi {
  T v = -inf<T>;
  maxi operator*(maxi b) const {
    return v < b.v ? b : *this;
  }
};

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> a(n);
  for (auto&& e : a) cin >> e;
  int res = inf<int>;
  {
    vector<int> ord(n);
    iota(begin(ord), end(ord), 0);
    sort(begin(ord), end(ord), [&](int i, int j) {
      return a[i] < a[j];
    });
    segtree<mini<int>> seg(n);
    for (int i : ord) {
      if (seg.fold(0, i).v != inf<int> and seg.fold(i + 1, n).v != inf<int>) {
        res = min(res, seg.fold(0, i).v + a[i] + seg.fold(i + 1, n).v);
      }
      seg.set(i, {a[i]});
    }
  }
  {
    vector<int> ord(n);
    iota(begin(ord), end(ord), 0);
    sort(begin(ord), end(ord), [&](int i, int j) {
      return a[i] > a[j];
    });
    segtree<mini<int>> seg(n);
    for (int i : ord) {
      if (seg.fold(0, i).v != inf<int> and seg.fold(i + 1, n).v != inf<int>) {
        res = min(res, seg.fold(0, i).v + a[i] + seg.fold(i + 1, n).v);
      }
      seg.set(i, {a[i]});
    }
  }
  if (res == inf<int>) {
    res = -1;
  }
  cout << res << '\n';
}