#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/all>
// using namespace atcoder;
#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rep1(i, n) for (ll i = 1; i <= n; ++i)
#define reps(i, s, e) for (ll i = s; i <= e; ++i)
#define rrep(i, n) for (ll i = n - 1; 0 <= i; --i)
#define all(v) v.begin(), v.end()
#define endl "\n"
template <class T>
bool chmax(T& a, const T& b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T& a, const T& b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
using ll = long long;
using ld = long double;
using cp = complex<ld>;
using pa = pair<ll, ll>;
using tup = tuple<ll, ll, ll>;
using vp = vector<pair<ll, ll> >;
using vtup = vector<tuple<ll, ll, ll> >;
using st = string;
using vs = vector<string>;
using vc = vector<char>;
using vvi = vector<vector<ll> >;
using vvc = vector<vector<char> >;
using vi = vector<ll>;
const ll MOD1 = 1000000007;
const ll MOD2 = 998244353;
const ll INF = (1ll << 60);

void init() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL), cout.tie(NULL);
  cout << fixed << setprecision(15);
}

int main() {
  init();

  ll n;
  cin >> n;
  vi a(n), lmn(n + 1), rmn(n + 1), lmx(n + 1), rmx(n + 1);

  lmn[0] = rmn[0] = INF;

  rep(i, n) cin >> a[i];

  rep(i, n) {
    lmn[i + 1] = min(lmn[i], a[i]);
    lmx[i + 1] = max(lmx[i], a[i]);
    rmn[i + 1] = min(rmn[i], a[n - i - 1]);
    rmx[i + 1] = max(rmx[i], a[n - i - 1]);
  }

  ll ans = -1;
  reps(i, 1, n - 1) {
    if (lmn[i] < a[i] && rmn[n - i - 1] < a[i]) {
      if (ans == -1) {
        ans = a[i] + lmn[i] + rmn[n - i - 1];
      } else {
        ans = min(ans, a[i] + lmn[i] + rmn[n - i - 1]);
      }
    }
    if (lmn[i] > a[i] && rmn[n - i - 1] > a[i]) {
      if (ans == -1) {
        ans = a[i] + lmn[i] + rmn[n - i - 1];
      } else {
        ans = min(ans, a[i] + lmn[i] + rmn[n - i - 1]);
      }
    }
  }

  cout << ans << endl;
}